[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__i18n__i18n.md

@@ -0,0 +1,64 @@
+# Module: `src/i18n/i18n.ts`
+
+> **Source**: `src/i18n/i18n.ts` (13 lines)
+> **Topo batch**: B2 (depends only on JSON data files)
+
+## Purpose
+
+Module-load-time initialisation of `i18next` with the `react-i18next` adapter. Imports the English and Ukrainian translation tables and registers them as the available `resources`. Exporting the configured singleton lets call sites use `useTranslation()` directly.
+
+## Public interface
+
+```ts
+export default i18n   // configured i18next instance
+```
+
+## Internal logic
+
+```ts
+i18n.use(initReactI18next).init({
+  resources: { en: { translation: en }, ua: { translation: ua } },
+  lng: 'en',
+  fallbackLng: 'en',
+  interpolation: { escapeValue: false },
+})
+```
+
+- `lng: 'en'` is hardcoded at boot. There is **no** runtime mechanism to detect the user's locale or to read a saved preference. Switching language at runtime works (via `i18n.changeLanguage(...)`) but the page reload always lands on English first.
+- `escapeValue: false` is the documented default for React (which already escapes JSX text).
+- Module side-effect at top level: `init()` runs as soon as `src/main.tsx` imports this file.
+
+## Dependencies
+
+- **Internal**: `./en.json`, `./ua.json` (JSON imports — Vite handles).
+- **External**: `i18next`, `react-i18next`.
+
+## Consumers (intra-repo)
+
+- `src/main.tsx` — side-effect import (`import './i18n/i18n'`).
+- Indirectly: every component that calls `useTranslation()` from `react-i18next` (e.g. `ConfirmDialog`, `HelpModal`, `JsonEditorDialog`, …).
+
+## Data models
+
+The two JSON resource files (`en.json`, `ua.json`) define the key namespace. Per `_docs/ui_design/README.md` §"Localization" and `_docs/legacy/wpf-era.md` §10, the SPA must support EN + UA at parity. Inspection of the JSON files (deferred to Step 4 verification) will confirm whether parity is held.
+
+## Configuration
+
+`lng: 'en'` and `fallbackLng: 'en'` are inlined. `localStorage` persistence (e.g., via `i18next-browser-languagedetector`) would be the natural Step 8 enhancement for "remember user choice"; deferred.
+
+## External integrations
+
+None.
+
+## Security
+
+`escapeValue: false` is correct in React but would be unsafe if any consumer rendered translation values via `dangerouslySetInnerHTML`. None do (verify in Step 4).
+
+## Tests
+
+None.
+
+## Notes / open questions
+
+- The `mission-planner/` sub-project does NOT use `react-i18next` — it has its own `LanguageContext` + raw `translations` table (see `00_discovery.md` §11 finding 8). The port to `src/features/flights/` should consume this module instead. Track for MP-B3.
+- Adding a third language is a one-line edit (`resources: { en, ua, <new> }`) plus a JSON file. Document the procedure in the final `solution.md`.