Add Python/FastAPI + PostgreSQL backend (Phase 1)

- server/: FastAPI app with SQLAlchemy models for sops, work_packages, comments
- Endpoints for SOP/WP upsert+list+get+delete and comment create+list;
  /api/feedback kept as an alias so the existing client keeps working
- Portable across engines (PostgreSQL prod, SQLite dev fallback)
- requirements.txt, .env.example, and server/README.md (Postgres + systemd)
- NGINX now proxies /api/ to the API (replaces the Power Automate hop;
  comments persist to SQL)
- Rewrite DEPLOYMENT.md for the API + database architecture
- Add .gitignore for venv/.env/sqlite

Phase 2 (wire the client apps to the API) is next.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

server/db.py

@@ -0,0 +1,41 @@
+"""Database engine and session setup.
+
+The connection string comes from the DATABASE_URL environment variable, e.g.
+    postgresql+psycopg://wpsuite:secret@db-host:5432/wpsuite
+
+If unset, it falls back to a local SQLite file so the API can be run and tested
+on any machine without Postgres. The schema is identical either way (SQLAlchemy
+handles the dialect differences).
+"""
+import os
+from sqlalchemy import create_engine
+from sqlalchemy.orm import sessionmaker, DeclarativeBase
+
+# Load a local .env if present (dev convenience). In production the DATABASE_URL
+# normally comes from the systemd unit's Environment / EnvironmentFile instead.
+try:
+    from dotenv import load_dotenv
+    load_dotenv()
+except Exception:
+    pass
+
+DATABASE_URL = os.getenv("DATABASE_URL", "sqlite:///./wpsuite.db")
+
+# SQLite needs this flag to be used from FastAPI's threadpool; Postgres ignores it.
+connect_args = {"check_same_thread": False} if DATABASE_URL.startswith("sqlite") else {}
+
+engine = create_engine(DATABASE_URL, connect_args=connect_args, pool_pre_ping=True, future=True)
+SessionLocal = sessionmaker(bind=engine, autoflush=False, autocommit=False, future=True)
+
+
+class Base(DeclarativeBase):
+    pass
+
+
+def get_db():
+    """FastAPI dependency that yields a session and always closes it."""
+    db = SessionLocal()
+    try:
+        yield db
+    finally:
+        db.close()