docs(project): sync docs with code and bump to 3.0.0

Prepare the 3.0.0 release:
- Bump the version in openapi.yaml and frontend/package.json to 3.0.0.
- Document the existing GET /health endpoint in openapi.yaml (served at the
  root, outside /api/v1) and refine the auth note.
- Add docs/REQUIREMENTS.md (product requirements, in English) and
  docs/ARCHITECTURE.md (system overview); remove the old Russian
  docs/Описание.md.
- Rewrite GO_PROJECT_STRUCTURE.md and FRONTEND_STRUCTURE.md to match the
  current code (dedup CLI, imagehash, real components/stores, Tailwind v4).
- Fix stale counts and references in CLAUDE.md and link the new docs from
  README.md.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/package.json

@@ -1,7 +1,7 @@
 {
 	"name": "frontend",
 	"private": true,
-	"version": "0.0.1",
+	"version": "3.0.0",
 	"type": "module",
 	"scripts": {
 		"generate:types": "openapi-typescript ../openapi.yaml -o src/lib/api/schema.ts",