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/dev/invariants.md

@@ -130,6 +130,15 @@ them explicit.
 - **Deletes and vector indexes:** `delete_where` and vector index creation still
   advance Lance HEAD inline because the required public Lance APIs are missing.
   Keep D2 and recovery coverage in place until those residuals are removed.
+- **Blob-column compaction:** Lance `compact_files` mis-decodes blob-v2 columns
+  under its forced `BlobHandling::AllBinary` read ("more fields in the schema
+  than provided column indices"), so `optimize` skips any table with a `Blob`
+  property — reporting `SkipReason::BlobColumnsUnsupportedByLance` (loud, not a
+  silent drop) behind the `LANCE_SUPPORTS_BLOB_COMPACTION` gate. Reads and writes
+  are unaffected; only space/fragment reclamation on blob tables is deferred.
+  Remove the skip when the upstream Lance fix lands — the
+  `lance_surface_guards.rs::compact_files_still_fails_on_blob_columns` guard
+  turns red on that bump to force it.
 - **Planner capability/stat surfaces:** cost-aware planning, complete
   capability advertisement, and explain-with-cost are roadmap. Do not describe
   them as implemented.