test(server): add integration tests for MCP tool functions

[clawtom]

Closes #5.

Adds tests/test_server_integration.py covering the three tool functions from the issue: vault_stats, vault_prediction_errors, and vault_search.

Approach

Each test uses a server_db fixture that:

1. Creates an initialised SQLite file in a tmp_path temp directory
2. Populates it with two test notes and chunks
3. Patches neurostack.schema.DB_PATH via pytest monkeypatch

Server tools import DB_PATH lazily (inside each function via from .schema import DB_PATH), so the patch is visible at call time — no Ollama, no real vault, no network required.

Coverage

vault_stats: valid JSON; required keys present (notes, chunks, embedded, embedding_coverage, etc.); counts match inserted test data; coverage values formatted as percentages.

vault_prediction_errors: valid JSON; required keys (total_flagged_notes, showing, errors); empty when no errors; surfaces inserted errors; error_type filter works; resolve clears errors.

vault_search (mode=keyword): valid JSON; finds relevant note by content; result items have required fields (path, title, section, score, snippet); no results for nonsense query; hybrid mode falls back gracefully when embedding service is unavailable.

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[clawtom]

Closing in favour of #7 which has a more complete commit message and test coverage. Apologies for the duplicate — a previous session submitted a partial version before completing.