feat: add Muse coding-plan provider

[yesme]

Track Meta Muse coding-plan quotas (5h prompts + weekly) from the same subscription snapshot muse /usage shows.

Why this shape

Meta publishes no aggregate usage endpoint for the coding plan (probed /v1/usage, /v1/billing, org usage/costs - all 404). Each poll sends one minimal streamed probe (POST /v1/responses with stream: true, input ping, max_output_tokens: 16) and extracts the inline subscription object. Verified against the live API:

{"subscription": {"tier": "pro",
  "weekly": {"resets_at": "1789344000", "used_percent": "12.5"},
  "window": {"resets_at": "1789078632", "used_percent": "34", "window_duration_mins": "300"}}}

Auth

Resolves as META_API_KEY -> providers.meta.api_key in the muse login file -> macOS Keychain / Linux keyring entry written by muse login. The Keychain lookup is deadline-bounded (15s + regression test) so an unanswered approval dialog can never block daemon startup.

Includes

• API client + types (string-or-number scalars, epoch s/ms, last-snapshot-wins SSE scan)
• Credential auto-detect (unix keychain/keyring, windows file) + probe-model resolution
• SQLite store (snapshots, quota values, reset cycles) + reset-cycle tracker + polling agent + daemon wiring
• 7 web endpoints, dashboard cards, menubar card, settings form, setup wizard, install.sh/ps1, docs/MUSE_SETUP.md, landing card

Verified

• ./app.sh --smoke green on this branch; tests/test_install.sh 27/27 (incl. 2 new Muse cases)
• End-to-end against the live API (daemon poll, store, cycles, all endpoints, dashboard tab, menubar)
• One pre-existing failure, unrelated: tools/perf-monitor TestMain_RestartFailureExitsWithError hangs in this dev environment because the test helper starts a real onwatch (found via PATH) and blocks forever on its output pipe. It fails identically with and without a repo-local binary, and involves no code touched by this PR.

[codecov]

Codecov Report

❌ Patch coverage is 48.54180% with 794 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
internal/web/muse_handlers.go	33.65%	256 Missing and 16 partials ⚠️
internal/store/muse_store.go	47.02%	160 Missing and 27 partials ⚠️
internal/tracker/muse_tracker.go	58.59%	47 Missing and 18 partials ⚠️
internal/web/handlers.go	14.89%	36 Missing and 4 partials ⚠️
internal/api/muse_credentials.go	50.68%	25 Missing and 11 partials ⚠️
main.go	18.60%	25 Missing and 10 partials ⚠️
internal/api/muse_token_unix.go	0.00%	33 Missing ⚠️
internal/api/muse_client.go	72.07%	25 Missing and 6 partials ⚠️
internal/agent/muse_agent.go	53.12%	26 Missing and 4 partials ⚠️
internal/api/muse_types.go	81.06%	14 Missing and 11 partials ⚠️
... and 3 more

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