fix(search,navigator,layout): fix live search retrieval, add full doc reader, resolve UI collisions, and eliminate mock test theatre

[spelech]

Summary

This PR addresses the root causes behind broken live search and document inspection discovered during live demo usage:

1. Live Search Failure & DB Isolation:

   • The test suite previously contaminated the production SQLite metadata database (index_cache.db), overriding vector_store_storage_path to point to a deleted temporary pytest directory (/tmp/pytest-of-steve/...) and resetting the collection to coll_v2.
   • Repaired metadata configuration to point to canonical persistent storage and collection.
   • Added automated database and vector store isolation in conftest.py via isolate_test_db fixture and dynamic SQLite engine path resolution in app/services/database/connection.py.
   • Fixed doc search retrieval across Qdrant, Chroma, and pgvector stores: documents with doc_type == 'doc' now match both doc and pdf types instead of silently omitting indexed PDFs.
   • Added end-to-end un-mocked backend verification test (test_execute_hybrid_search_end_to_end_real) testing real vector and lexical BM25 indexing and retrieval.

2. Full Document Reader in Code Navigator:

   • Extended resolve_safe_path() in app/services/file_reader.py to support root-level project documentation (e.g. README.md) when repo == '__all__'.
   • Built NavigatorDocReader.tsx with Markdown formatting (headers, inline code, fenced syntax blocks, lists, blockquotes) and raw source table view with line numbers and file statistics.
   • Updated NavigatorInspector.tsx with tab toggling between Symbol Intelligence and Full File Content, auto-rendering the document reader for non-code files.
   • Added empty outline state with explicit 'Read Full Document' action button in NavigatorOutline.tsx.

3. Responsive UI Layout & Zero Collisions:

   • Resolved sibling AABB bounding box collision in search bars by switching from absolute overlapping icons to flexbox layout.
   • Enforced responsive vertical stacking on mobile viewports (<900px) with word-breaking, wrapping, and container bounds safeguards.
   • Integrated playwright-layout-inspector checks across desktop and mobile in both e2e/navigator.spec.ts and e2e/layout-inspector.spec.ts, asserting toHaveNoLayoutOverflow() and toHaveNoElementCollisions().

4. Eliminating Mock Test Theatre:

   • Replaced fragile mocks with real execution tests across backend and frontend suites.
   • All 517 Pytest backend tests pass.
   • All 293 Vitest frontend unit tests pass.
   • All 16 Playwright Navigator E2E tests and 18 Layout Inspector E2E tests pass across Desktop Chrome and Mobile Pixel 5.