Migrate to PostgreSQL + add FastAPI webapp for Coolify deploy

Backend migration:
- Replace pyodbc/SQL Server with psycopg2/PostgreSQL throughout
- Rewrite Database class with portable SQL: SERIAL, ON CONFLICT, NOW()
- Lowercase table names (rip_help_files, rip_help_sections) - Postgres convention
- libpq connection string format in HELP_DB_CONN

Webapp (webapp/):
- FastAPI app: GET /, GET /images/<f>, GET /home-image, GET /api/sections,
  POST /api/keywords/<code>, GET /healthz
- Jinja2 template extracted from generate_html.py with HTTP image URLs
- Direct keyword save to DB (no JSON download detour)
- Same prefix scoping as CLI tools (?prefix=RIP)

Deployment:
- Dockerfile (python:3.12-slim + uvicorn)
- docker-compose.yml for local dev
- requirements-webapp.txt (minimal, no Windows-only deps)
- .dockerignore excludes pipeline scripts and BAT files
- README updated with webapp section and Coolify deploy guide

Also: switch AI model to claude-haiku-4-5 (~3x cheaper, same quality for this task)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.env.example

@@ -1,5 +1,6 @@
 REM Copy to .env and fill in real values. .env is gitignored.
-REM Loaded by .bat файловете чрез: for /f "delims=" %%a in (.env) do set "%%a"
+REM Loaded by .bat файловете чрез: call _load_env.bat
+REM HELP_DB_CONN е libpq формат за PostgreSQL.
 
 ANTHROPIC_API_KEY=sk-ant-api03-XXXXXXXXXXXXXXXXXXXXXXXXX
-HELP_DB_CONN=DRIVER={ODBC Driver 18 for SQL Server};TrustServerCertificate=yes;SERVER=host,port;DATABASE=db;UID=user;PWD=password
+HELP_DB_CONN=host=192.168.88.18 port=5432 dbname=rip_help_system user=postgres password=YOUR_PASSWORD