Add repair-semantic-queue command + post-update bridge for the OV poison loop (#2734)

[Kashkovsky]

Temporary bridge so users stuck on the current pinned OpenViking can drain/avoid the semantic-queue poison loop (#2734) without waiting for the upstream release.

A memory file reindexed with mode=semantic_and_vectors enqueues a directory-level context_type="memory" semantic message; OpenViking's _process_memory_directory lists the file, fails, and the AGFS-persisted message re-enqueues forever — surviving a server restart and stalling reindex --wait / memory writes. threadnote 1.4.1 bounded its own waits (no more 31-min hang), but couldn't clear the cause.

New command threadnote repair-semantic-queue [--apply]:

• Patches the installed OpenViking semantic_processor.py to skip non-directory/missing memory URIs (the upstream #2735 / PR volcengine/OpenViking#2735 guard), then restarts the server so a stuck message drains on the next dequeue.
• Idempotent + scoped to "OV unfixed": no-op when a stat(dir_uri) guard (or a prior hot-fix marker) is already present. Keeps a .threadnote-bak, and compile-checks the patched source (python -m py_compile) before writing.
• Locates the package from the OV server's venv, common uv/pipx roots, or the venv python; override with THREADNOTE_OPENVIKING_SEMANTIC_PROCESSOR.

Post-update migration (introducedIn: 1.4.3): offers the patch on threadnote update with the usual consent prompt (auto-runs only on --yes/interactive-confirm), after ensurePinnedOpenVikingInstalled, so it patches the freshly-installed OV.

Marked for removal: a REMOVE-WHEN note ties this to bumping DEFAULT_OPENVIKING_VERSION to an OpenViking release containing #2735 — at which point the command no-ops and the migration can be dropped. The real fix remains the pin bump + existing upgrade path.

The pure patcher logic is what's tested.

Test plan

• npm run typecheck, npm run lint, npm test (292 tests / 25 files) green.
• New semantic_queue_repair.test.ts: patch inserts the guard at the right indent before ls(dir_uri); idempotent (marker → already-fixed); upstream stat(dir_uri) guard → already-fixed; no-anchor when the ls call / method is absent.
• Validated the built command end-to-end against the real installed OV 0.4.4 (already-fixed path) and a clean copy via the env override (would-patch dry run). The full apply+restart path was validated earlier via the equivalent standalone script on this machine.