feat(pinterest): add Pinterest adapter suite

[yeeway0609]

Description

Adds a pinterest adapter covering both read and write surfaces — 19 commands over Pinterest's
internal resource API (POST /resource/<Name>Resource/<action>/, form-urlencoded source_url +
data, X-CSRFToken + X-Pinterest-PWS-Handler, feeds paginated by resource_response.bookmark).
Reads work on a logged-out session because Pinterest issues a csrftoken to anonymous visitors too;
only the writes need a login.

search-pins / search-boards / search-users        pin / user / user-pins / user-boards
board-pins / board-sections / download            save / pin-create / pin-update / pin-delete
board-create / board-update / board-delete        board-section-create / board-section-delete

Boards are addressed by <username>/<slug>, a board URL, or the numeric boardId from
user-boards; sections by slug or id. Deletes require --confirm and otherwise name the resolved
target and exit non-zero. --limit and flag combinations are validated before any request goes
out.

Related issue:

Type of Change

• 🐛 Bug fix
• ✨ New feature
• 🌐 New site adapter
• 📝 Documentation
• ♻️ Refactor
• 🔧 CI / build / tooling

Checklist

• I ran the checks relevant to this PR
• I updated tests or docs if needed
• I included output or screenshots when useful

Documentation (if adding/modifying an adapter)

• Added doc page under docs/adapters/ (if new adapter)
• Updated docs/adapters/index.md table (if new adapter)
• Updated sidebar in docs/.vitepress/config.mts (if new adapter)
• Updated README.md / README.zh-CN.md when command discoverability changed
• Used positional args for the command's primary subject unless a named flag is clearly better
• Normalized expected adapter failures to CliError subclasses instead of raw Error

Screenshots / Output

All 19 commands live-verified against a logged-in account; everything created during verification
was removed afterwards with the adapter's own delete commands.

$ opencli pinterest search-pins "nordic interior" --limit 2 -f json
[
  { "pinId": "703756189347071", "title": "Scandinavian Living Room Design- On a Budget", "pinner": "kathareineke",
    "board": "Wohnzimmer", "imageUrl": "https://i.pinimg.com/originals/36/5d/0a/365d0a842973e6bd8e009588f317cc86.png",
    "url": "https://www.pinterest.com/pin/703756189347071/" },
  { "pinId": "9781324187251346", "title": "", "pinner": "fabianamiyai", "board": "Estilo Escandinavo",
    "url": "https://www.pinterest.com/pin/9781324187251346/" }
]

$ opencli pinterest user yeeway0609 -f json
[ { "username": "yeeway0609", "fullName": "Alex", "followerCount": 11, "followingCount": 11,
    "interestFollowingCount": 4, "pinCount": 2254, "boardCount": 10 } ]

$ opencli pinterest board-sections yeeway0609/art -f json
[ { "sectionId": "5278516809142679899", "title": "Pixel", "slug": "pixel", "pinCount": 9 },
  { "sectionId": "5064878735868608231", "title": "Anime", "slug": "anime", "pinCount": 62 } ]

Full write cycle, on a scratch board created for the run:

$ opencli pinterest board-create "OpenCLI adapter test" --privacy secret -f json
[ { "boardId": "720576077820063683", "name": "OpenCLI adapter test", "privacy": "secret" } ]

$ opencli pinterest pin-create "https://images.unsplash.com/photo-1552053831-71594a27632d?w=1200" \
    --board yeeway0609/opencli-adapter-test --section dog --title "OpenCLI dog pin" -f json
[ { "pinId": "720576009177385394", "board": "OpenCLI adapter test", "title": "OpenCLI dog pin" } ]
  → pin 720576009177385394 section = "Dog"

$ opencli pinterest save 3096293491909700 --board yeeway0609/opencli-adapter-test --section dog -f json
[ { "pinId": "720576009177385389", "sourcePinId": "3096293491909700", "board": "OpenCLI adapter test" } ]

$ opencli pinterest save 3096293491909700 --board yeeway0609/opencli-adapter-test --section nope
error: ARGUMENT  No section matching "nope" on this board
  help: Pass a section slug or id — available: dog (3709610207346291072), cats (3709593716249242688)

$ opencli pinterest board-delete yeeway0609/opencli-adapter-test
error: ARGUMENT  Refusing to delete board "OpenCLI adapter test" (7 pins) without --confirm

$ opencli pinterest board-delete yeeway0609/opencli-adapter-test --confirm -f json
[ { "boardId": "720576077820063683", "name": "OpenCLI adapter test", "pinCount": 7, "deleted": true } ]

Field clearing and the delete preview, on a second scratch board:

$ opencli pinterest pin-update 720576009177386379 --description "" -f json
$ opencli pinterest pin 720576009177386379 -f json
[ { ..., "description": "", "link": "https://example.com/" } ]      # description cleared

$ opencli pinterest pin-update 720576009177386379 --link ""
error: AUTH_REQUIRED  Pinterest refused this write: 你無權存取該資源。   # Pinterest owns a scraped pin's link

$ opencli pinterest pin-delete 720576009177386379
error: ARGUMENT  Refusing to delete pin 720576009177386379 "Review test pin" from board "OpenCLI review test" without --confirm

Notes for review:

• Sections can only be set by a follow-up move. PinResource/create and RepinResource/create
  accept a section key, answer HTTP 200, and file the pin at the board root anyway; only
  PinResource/update honours one, under board_section_id (a section_id key is likewise
  accepted and ignored). So save --section / pin-create --section create then move, and a failed
  move raises CommandExecutionError naming the pin already created instead of reporting success.
  Placement was verified on each pin's own section field, not the section's cached pin_count.
• Board URLs are percent-decoded before use. Pinterest hands out encoded slugs for non-ASCII
  board names (/u/test-board-caf%C3%A9-%E6%B8%AC%E8%A9%A6/) and posting one verbatim answers
  HTTP 404. Slugs compare Unicode-normalized, so an NFD-composed accent still matches.
• Identifiers only. A board display name is rejected rather than guessed at, since a bare name
  cannot say which account owns the board; BoardResource accepts board_id, which is what makes
  the numeric form work, and the board it returns is reused so that path costs no extra round trip.
  A /pin/<id>/ or /search/ URL is reported as such instead of being parsed as the board
  pin/<id>, and a board ref passed where a username belongs says so rather than 404ing on a
  mangled name.
• Empty string clears, omitted leaves alone. Optional text flags carry no default, so
  --description "" clears the field while omitting it changes nothing. Pinterest refuses link
  edits on pins it scraped and answers 401 for that, so its own message is surfaced
  (Pinterest refused this write: 你無權存取該資源) rather than only "log in".
• A 403 on a read is a rejected request (CommandExecutionError, hinting at a stale CSRF token); a
  403 on a write is AuthRequiredError. page.goto can resolve before the csrftoken cookie
  exists, so the in-page script waits for it instead of firing a doomed request.
• save without --board posts a boardless repin, which Pinterest files under "Quick saves".
  pin-create cannot do that — a new pin always needs a board. Pinterest also overrides
  --description for scraped pins.
• user exposes interestFollowingCount because Pinterest's following_count bundles followed
  people and topics.

clis/pinterest/*.test.js passes 131 / 131 (ref and board-id parsing, the auth / CSRF / HTTP-error
ladder, bookmark pagination with dedup, promoted-pin filtering, the --confirm gate on all three
deletes, the section path (no section key on create, board_section_id on the follow-up, a failed
move surfacing the pin id, a display title not resolving, --section without --board rejected),
and that a board id is not re-fetched. Full suite 6258 passed;
tsc --noEmit clean; opencli validate 0 errors; check:typed-error-lint and
check:silent-column-drop both new=0; check-doc-coverage.sh --strict 174/174.