feat: bulk= keyword param on ingest_turn (#194)

[robotrocketscience]

Summary

Additive, keyword-only bulk: bool = False on ingest_turn.

When bulk=True, duplicate-sentence record_corroboration writes are skipped — the only currently-redundant per-turn side effect inside a multi-turn batch. Canonical beliefs row and v2.0 ingest_log row are always produced; final belief state is identical either way.

Default-off preserves prior behaviour for every existing caller.

Scope decisions

• bulk is keyword-only (positional pass rejected) — guards against future args being inserted before it and keeps the call site self-documenting.
• The issue body listed three "likely candidates" to skip (per-turn promotion checks, FTS5 commits, telemetry rows). None of those exist as code today, so the implementation skips only the side effect that does exist (record_corroboration on duplicates). Docstring notes it's reserved for future per-turn-cost reductions as new side effects land.
• No flush() / context-manager — there is nothing buffered to flush at present. SQLite autocommit at the store layer is fine for current scale.

Tests

tests/test_ingest_bulk.py (new):

• default-off
• keyword-only enforcement
• unique-sentence input → identical state for bulk=True vs bulk=False
• duplicate-sentence input → identical beliefs, divergent belief_corroborations
• bulk=True still writes ingest_log (v2.0 source-of-truth invariant)

Full local run: 1728 passed, 8 skipped.

Closes #194.