fix(lancedb): detect schema type drift and add cascade rebuild recovery

[gloryfromca]

Problem — the root cause behind #337

verify_business_schemas (the startup guard) only compared column names against the current schema. A column whose on-disk Arrow type had drifted — name unchanged — sailed through and detonated much later, deep inside merge_insert, as the notoriously opaque:

RuntimeError: lance error: LanceError(IO): Execution error: Spill has sent an error, poll.rs:291:44

This is exactly #337: an episode.subject_vector column left as string (or null) by an older build, while the current schema declares a 1024-d fixed_size_list. Writing a real vector into that column is a pyarrow type error that lance wraps as the "Spill" IO error.

Verified

• Reproduced byte-identically: a drifted subject_vector (string and null) column + a real 1024-d vector through the real LanceRepoBase.upsert() path yields the exact cascade worker fails to index episodes: LanceDB Spill has sent an error (IO) #337 error; a correctly-typed table accepts the same records.
• No lancedb version produces the bad column (checked 0.13→0.34: ≤0.19 raise TypeError, 0.20+ render the correct fixed_size_list), and lance never silently adds a mistyped column — so the drift originates from a build that declared the field differently, and the guard is what should have caught it at startup.

Changes

1. Type-aware verify_business_schemas — compare each shared column's Arrow type against schema.to_arrow_schema() (the exact schema get_table builds tables from, so a healthy table never false-positives). On drift the startup error now names the drifted column and both types instead of the runtime Spill.

2. everos cascade rebuild — the safe recovery from a drifted/corrupt index:

• drops the business LanceDB tables and re-indexes from markdown (the source of truth);
• skips the verify guard (whose whole point is the drift it would otherwise trip on at startup — chicken-and-egg);
• unlike rm -rf ~/.everos/.index/lancedb, re-populates already-done entries (reset_all clears the cascade queue so every md file re-enqueues) — a bare rm of the lancedb dir leaves the queue marked done and the index comes back empty;
• unlike rm -rf ~/.everos/.index, preserves unprocessed_buffer (messages received but not yet extracted — not rebuildable from md).

Tests

• test_verify_schemas.py — healthy tables pass (false-positive guard); subject_vector as string/null raises with type_drift; missing column raises (unchanged); drop_business_tables drops + recreates the correct vector type. The type-drift tests were confirmed to fail without the fix (old guard DID NOT RAISE).
• test_md_change_state.py — reset_all clears every row regardless of status; noop on empty.
• test_cascade_cli_integration.py — cascade rebuild runs despite a drift that trips a normal command's startup verify, recreates the table with the correct type, and re-indexes md from scratch.

Full unit suite + make lint (ruff, import-linter, datetime, openapi) green.

Fixes #337.