[AZ-447] autodev Steps 1-4 baseline: docs, tests, refactor specs

Captures the full output of autodev existing-code Phase A through
Step 4 (Code Testability Revision) for the Azaion UI workspace:

- Step 1 Document: _docs/02_document/ (FINAL_report, architecture,
  glossary, components/, modules/, diagrams/, system-flows,
  module-layout) plus _docs/00_problem/ + _docs/01_solution/ +
  _docs/legacy/ + _docs/how_to_test + README.
- Step 2 Architecture Baseline: architecture_compliance_baseline.md.
- Step 3 Test Spec: _docs/02_document/tests/ (environment,
  test-data, blackbox/performance/resilience/security/
  resource-limit tests, traceability-matrix), enum_spec_snapshot,
  expected_results/results_report.md (98 rows), plus the
  run-tests.sh + run-performance-tests.sh runners.
- Step 4 Code Testability Revision: 01-testability-refactoring/
  run dir (list-of-changes C01-C07, deferred_to_refactor,
  analysis/research_findings + refactoring_roadmap) and the 7
  child task specs AZ-448..AZ-454 under _docs/02_tasks/todo/
  plus _dependencies_table.md.
- _docs/_autodev_state.md pins the cursor at Step 4 / refactor
  Phase 4 entry so /autodev resumes cleanly.

Epic AZ-447 (UI testability gates) tracks the 7 child tasks that
will land in subsequent commits.

Co-authored-by: Cursor <cursoragent@cursor.com>

_docs/02_document/modules/src__hooks__useDebounce.md

@@ -0,0 +1,55 @@
+# Module: `src/hooks/useDebounce.ts`
+
+> **Source**: `src/hooks/useDebounce.ts` (12 lines)
+> **Topo batch**: B1 (leaf)
+
+## Purpose
+
+Generic React hook that delays propagation of a rapidly-changing value to its consumers, used to throttle search inputs against the backend.
+
+## Public interface
+
+```ts
+export function useDebounce<T>(value: T, delay: number): T
+```
+
+Returns the latest `value` only after `delay` milliseconds have elapsed without any further change. Generic in `T`, so callers can debounce strings, numbers, or any reference value (referential identity matters; see notes).
+
+## Internal logic
+
+`useState<T>(value)` for the debounced output; `useEffect` registers a `setTimeout(setDebounced, delay)` and returns a `clearTimeout` cleanup. The effect re-runs whenever `value` or `delay` changes — each new input value cancels the pending timeout from the previous render and starts a fresh one.
+
+## Dependencies
+
+- **Internal**: none.
+- **External**: `react` (`useState`, `useEffect`).
+
+## Consumers (intra-repo)
+
+- `src/features/annotations/MediaList.tsx` — debounces the media-name search input.
+- `src/features/dataset/DatasetPage.tsx` — debounces the dataset name-search filter (specified as 400ms in `_docs/ui_design/README.md` §"Dataset Explorer", but the actual delay is set by the caller).
+
+## Data models
+
+None.
+
+## Configuration
+
+None.
+
+## External integrations
+
+None.
+
+## Security
+
+None.
+
+## Tests
+
+None.
+
+## Notes / open questions
+
+- The hook compares values by referential equality (`useEffect` deps array). Passing a fresh object literal each render — e.g. `useDebounce({ q }, 300)` — would re-trigger the timer endlessly. Current callers pass primitives only; safe.
+- No "leading edge" / "trailing edge" / "max wait" knobs. Adequate for the two current consumers; if/when richer behaviour is needed, prefer `useDebouncedCallback` from a library over extending this module.