fix(optimize): skip blob-bearing tables to avoid Lance compaction crash (#138)

* test(optimize): pin Lance blob-column compaction failure as a surface guard

Lance compact_files mis-decodes blob-v2 columns under its forced BlobHandling::AllBinary read ("more fields in the schema than provided column indices"), failing even a pristine uniform-V2_2 multi-fragment blob table; reads use descriptor handling and are unaffected.

Guard 10 reproduces this and is self-retiring: it turns red on the Lance bump that fixes the bug, forcing LANCE_SUPPORTS_BLOB_COMPACTION to flip.

* fix(optimize): skip blob-bearing tables instead of crashing compaction

omnigraph optimize aborted the whole sweep when any node/edge table had a Blob property: Lance compact_files cannot decode blob-v2 columns under AllBinary (the column-index error pinned by the surface guard). Skip blob-bearing tables behind a LANCE_SUPPORTS_BLOB_COMPACTION gate and report them via TableOptimizeStats.skipped / SkipReason (surfaced in the CLI and a tracing::warn) instead of erroring, which also isolates the failure so the other tables still compact.

Reads/writes are unaffected; only fragment/space reclamation on blob tables is deferred until the upstream Lance fix. Adds a maintenance.rs regression test (validated red with the column-index symptom before the fix, green after), a concise v0.6.1 release note, and updates docs (maintenance, cli-reference, AGENTS capability matrix, invariants Known Gaps, lance.md audit, constants).

* refactor(optimize): make TableOptimizeStats and SkipReason non_exhaustive

Both are returned result types, never built by callers, so #[non_exhaustive] makes this the last field/variant addition that can break downstream literal construction and keeps future ones non-breaking (review feedback on the public-field addition). The v0.6.1 Compatibility Notes call out the source-level change.

Also drops the now-stale "RED today / GREEN after the fix lands" narration in the optimize_skips_blob_table_and_reports_skip test (historical regression context now that the fix is in this branch), and folds in the expanded v0.6.1 release note.

* chore(release): bump workspace to v0.6.1

Coherent version bump to accompany the v0.6.1 release note: all five crate manifests + path-dependency constraints, Cargo.lock, the AGENTS.md surveyed-version line, and openapi.json info.version move 0.6.0 -> 0.6.1. Matches the established release pattern (#118 landed the v0.6.0 note + bump together) and resolves the Codex/Devin review flag that a v0.6.1 note without a bump leaves CARGO_PKG_VERSION reporting 0.6.0 and mixed package versions.

docs/user/maintenance.md

@@ -7,7 +7,8 @@
 - Lance `compact_files()` on every node + edge table on `main`.
 - Rewrites small fragments into fewer large ones; old fragments remain reachable via older manifests.
 - Bounded by `OMNIGRAPH_MAINTENANCE_CONCURRENCY` (default 8).
-- Returns `[TableOptimizeStats { table_key, fragments_removed, fragments_added, committed }]`.
+- Returns `[TableOptimizeStats { table_key, fragments_removed, fragments_added, committed, skipped }]`.
+- **Blob tables are skipped.** A table that declares any `Blob` property is not compacted: it is reported with `skipped: Some(BlobColumnsUnsupportedByLance)` (and logged via `tracing::warn`) instead of compacted, and the rest of the sweep proceeds normally. The current Lance `compact_files` mis-decodes blob-v2 columns under its forced `BlobHandling::AllBinary` read; **reads and writes are unaffected** — only compaction is. This is gated by `LANCE_SUPPORTS_BLOB_COMPACTION` (`db/omnigraph/optimize.rs`) and removed when the upstream Lance fix lands (see [docs/dev/lance.md](../dev/lance.md)). Consequence: fragment count and deleted-row space on blob tables are not reclaimed until then; query results are never affected.
 
 ## `cleanup_all_tables(db, options)` — destructive