feat(graphile-llm): auto-embed unifiedSearch text for hybrid vector+keyword search

[pyramation]

Summary

When graphile-llm is active with a configured embedder, unifiedSearch: "text" now automatically embeds the text and includes pgvector in the RRF rank fusion — zero client changes, zero new fields.

Architecture (resolver-wrapper pattern):

Client: unifiedSearch: "HIPAA compliance"  (String — schema unchanged)
                    ↓
LlmTextSearchPlugin resolver wrapper (async, pre-plan):
  1. Detects unifiedSearch string in args.where
  2. Calls embedder("HIPAA compliance") → [0.1, 0.3, ...]
  3. Transforms: args.where.unifiedSearch = { __text: "HIPAA compliance", __vector: [0.1, ...] }
                    ↓
unifiedSearch apply function (sync, plan-time):
  - typeof val === 'object' && val.__text → extracts text + vector
  - Fans out __text to tsv, BM25, trgm (existing behavior)
  - Passes __vector to pgvector adapter's buildFilterApply
  - All WHERE clauses combined with OR
  - RRF fuses all 4 rank lists into normalized [0,1] searchScore

Graceful degradation:

• Embedder returns null (quota exceeded) + text adapters exist → falls back to text-only search (no error)
• Embedder returns null + NO text adapters (vector-only table) → throws explicit error

Key changes:

• graphile-search/plugin.ts apply function: accepts { __text, __vector } object in addition to plain String
• graphile-llm/text-search-plugin.ts embedTextInWhere: detects unifiedSearch key, embeds text, transforms to object shape
• Resolver wrapper now wraps tables with searchable columns (not just vector-only)
• hasTextAdapters parameter threads through for degradation logic

Tests: 12 unit tests (no DB) + 4 integration tests with mock LLM plugin verifying pgvector participates in RRF fusion when embedding is injected.

Closes #1054

Link to Devin session: https://app.devin.ai/sessions/4a9f098c74fb4cb6a9b6868fcff321db
Requested by: @pyramation

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