fix: bootstrap forward-references for v39-v41 schema replay

[lanceretter]

Summary

Three column-with-index forward references in the embedded schema blob were missing from applyForwardReferenceBootstrap, so any brain at config.version < 39 (Postgres) or < 41 (PGLite) wedges before the migration runner can advance.

Reproduced end-to-end on a PlanetScale Postgres brain stuck at config.version=34 trying to upgrade to v0.30.0:

ERROR: column "effective_date" does not exist
ERROR: column cc.modality does not exist

After hitting these errors, gbrain search and gbrain reindex-frontmatter both fail because the same columns are referenced by query-path code, but you can't get past the migration step to add them.

The schema-blob references that crash before migrations run

• v39 (multimodal_dual_column_v0_27_1):

  CREATE INDEX idx_chunks_embedding_image
    ON content_chunks USING hnsw (embedding_image vector_cosine_ops)
    WHERE embedding_image IS NOT NULL;

• v41 (pages_recency_columns):

  CREATE INDEX pages_coalesce_date_idx
    ON pages ((COALESCE(effective_date, updated_at)));

What's in this PR

• Postgres engine (src/core/postgres-engine.ts): probe + branch for v39 (modality, embedding_image) — was entirely missing on Postgres, so Postgres brains pre-v39 hit the wedge that PGLite already protected against. PGLite's probe at line 273 had embedding_image_exists; Postgres did not.
• Both engines: probe + branch for v40+v41. Bootstraps all five additive pages columns (emotional_weight, effective_date, effective_date_source, import_filename, salience_touched_at) gated on effective_date_exists as the proxy.
• test/schema-bootstrap-coverage.test.ts: extends REQUIRED_BOOTSTRAP_COVERAGE with the six new columns AND the pre-test DROP block so both the per-target assertion test and the end-to-end "bootstrap + SCHEMA_SQL replay" test exercise the new coverage.

Bootstrap stays additive-columns-only. Indexes are left to schema replay / migrations as before — adding indexes in bootstrap duplicates responsibilities and worsens lock/surprise risk.

Test plan

• bun test test/schema-bootstrap-coverage.test.ts — all 5 tests pass (was 5 before, still 5; expanded coverage caught no regressions in the existing assertions).
• bun run typecheck — clean.
• e2e Postgres bootstrap (test/e2e/postgres-bootstrap.test.ts) on a real Postgres — couldn't run locally without DATABASE_URL to a fresh test DB, but the same bootstrap function the PGLite test exercises is now mirrored on Postgres.

Companion to #740

#740 fixes three independent v0.30.0 upgrade-path bugs (deps, UNSAFE_TRANSACTION, missing connect). This PR is the structural follow-up flagged in #740's body — it closes the bootstrap gap so future brains crossing v0.27/v0.29.1 don't need the same manual ALTER TABLE ADD COLUMN IF NOT EXISTS workaround.

The two PRs are independent: either can land first.

🤖 Generated with Claude Code

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