feat(navigation): verify editor selection mutations

[dubesinhower]

Navigation MVP slice N4

Adds semantic clear/add/remove selection operations for an exact KiCad editor context, with stable-KIID target validation and result-derived readback.

Why this belongs in the MVP

Navigation needs a safe way to express selection intent without exposing raw actions or treating a successful transport round trip as proof that KiCad changed state.

Dependency

• Depends on feat(navigation): resolve exact editor targets #398 (N3 exact target resolution), which depends on feat(navigation): observe exact editor selection #397 and feat(navigation): observe editor capabilities #396.
• Uses the typed Priority 0 IPC foundation through fix(ipc): bind operations to the requested board #390 and does not depend on draft fix(board): refuse stale locked file fallbacks #391.
• Tracks provisional public naming and compatibility in Design Priority 1 semantic editor navigation MVP #395; this PR remains draft.

Behavior

• Uses typed ClearSelection, AddToSelection, and RemoveFromSelection commands only.
• Requires an exact project/document/editor/sheet context; schematic instances are addressed by canonical KIID path.
• Resolves every add/remove KIID in the explicit saved structure before sending a mutation.
• Reads the exact selection before and after the command and requires the complete observed set to equal the requested transition.
• Returns before/after stable object identities and explicit live readback evidence.
• Refuses duplicate/empty IDs, stale/missing targets, wrong projects/documents/sheets, closed editors, unsupported commands/object decoding, and post-operation mismatch.

Intentionally unsupported here

• Selection does not imply viewport reveal, centering, fitting, document activation, or cross-probing.
• No raw RunAction API is exposed.

Verification

• cargo fmt --all -- --check
• cargo test -p konnect-ipc --test mock_server_test — 47 passed, 1 ignored
• cargo test -p konnect-core editor_navigation --lib — 12 passed
• cargo test -p konnect-core --lib — 943 passed, 9 ignored
• cargo test --workspace --all-targets — passed (live/environment-only tests remained ignored)
• cargo clippy --workspace --all-targets -- -D warnings
• cargo clippy -p konnect-ipc --tests -- -D warnings after the final exact-list comparison tightening
• xtask fix-doc-counts --check — 21 toolsets, 225 registered, 232 total
• git diff --check

Hermetic transport tests exercise clear, add, and remove success; exact document headers; duplicate validation before transport; wrong/stale inherited context refusals; typed unsupported mapping; and a successful mutation response followed by unchanged selection, which returns readback_mismatch.

Remaining risks

• KiCad 10's stable schematic protobuf cannot decode selected symbols, so symbol selection remains explicitly unsupported instead of unverifiable.
• KiCad selection replies have no document header; bounded before/after GetOpenDocuments checks are the available freshness boundary and are not atomic.
• No live endpoint was available, so real-GUI success is not claimed.

[neusse]

Superseded by #493, which reconstructs this N4 change directly on the now-merged N3 baseline (#492 / current main). The replacement preserves the original implementation and @dubesinhower authorship, resolves the one current-main structured-error conflict without dropping either behavior, and has passed the full local gate. Closing this cumulative branch so review and CI follow the minimal sequential PR.