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.

crates/omnigraph-cli/src/main.rs

@@ -3011,18 +3011,19 @@ async fn main() -> Result<()> {
                         "fragments_removed": s.fragments_removed,
                         "fragments_added": s.fragments_added,
                         "committed": s.committed,
+                        "skipped": s.skipped.map(|r| r.as_str()),
                     })).collect::<Vec<_>>(),
                 });
                 print_json(&value)?;
             } else {
                 println!("optimize {} — {} tables", uri, stats.len());
                 for s in &stats {
-                    if s.committed {
+                    if let Some(reason) = s.skipped {
+                        println!("  {:<40} skipped ({reason})", s.table_key);
+                    } else if s.committed {
                         println!(
                             "  {:<40} frags {} → {} ✓",
-                            s.table_key,
-                            s.fragments_removed + s.fragments_added - s.fragments_added,
-                            s.fragments_added
+                            s.table_key, s.fragments_removed, s.fragments_added
                         );
                     } else {
                         println!("  {:<40} no-op", s.table_key);