Remove legacy query facades (query_facade.py, pathfinding_facade.py, query_service.py)

[aaronsb]

Context

With GraphFacade (PR #274) and batch hydration (PR #276) merged, the old pre-acceleration query layer is dead code:

File	Lines	Status
api/app/lib/query_facade.py	681	Superseded by graph_facade.py
api/app/lib/pathfinding_facade.py	654	Superseded by graph_facade.find_paths()
api/app/lib/query_service.py	~200	Superseded by direct client.graph.* calls

These were the intermediate abstraction layer between routes and AGEClient. Routes now call client.graph.* directly (for topology) and _hydrate_grounding_batch() (for grounding/confidence).

Steps

1. Audit all imports of QueryFacade, PathfindingFacade, QueryService across the codebase
2. Verify no remaining callers (routes, services, tests)
3. Delete the files
4. Remove any test files that only test the old facades
5. Run full test suite to confirm

~1,500 lines removed

References

• Phase 5e in .claude/todo-adr-201-graph-accel.md
• PR feat: unified GraphFacade with graph_accel integration (ADR-201 Phase 5b) #274 (GraphFacade), PR feat: generation-aware hydration caches (ADR-201 Phase 5f) #276 (batch hydration)

[aaronsb]

Partial completion

Deleted pathfinding_facade.py (654 lines) and query_service.py (~350 lines) — both fully dead code with zero callers.

query_facade.py (GraphQueryFacade) cannot be deleted yet. It has ~15 active callers:

• source_embedding_worker.py — 10+ calls to facade.execute_raw()
• vocab_consolidation.py — facade.execute_raw()
• category_refresh.py — facade.match_vocab_categories()
• vocabulary.py routes — facade.match_vocab_types()
• polarity_axis.py — facade.match_concepts(), facade.execute_raw()
• database.py routes — facade.count_concepts(), facade.execute_raw()

GraphQueryFacade provides namespace-safe Cypher execution (execute_raw, match_concepts, match_vocab_types, etc.) — these are a different layer from GraphFacade's topology operations.

Migrating these callers is a separate task that involves either:

• Adding equivalent methods to GraphFacade
• Moving the namespace-safe Cypher utilities to a shared location

Keeping this issue open for the remaining work.

[aaronsb]

Reopening — query_facade.py still has ~15 active callers that need migration.