Add Amnezia Web Panel source with PostgreSQL 17 storage.

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

.env.example

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+# Panel
+APP_PORT=5000
+SECRET_KEY=change-me-to-a-long-random-string
+
+# PostgreSQL 17
+POSTGRES_USER=amnezia
+POSTGRES_PASSWORD=amnezia
+POSTGRES_DB=amnezia_panel
+POSTGRES_PORT=5432
+
+# Used by the panel process (local run or Docker)
+# Docker Compose sets this automatically to point at the db service.
+DATABASE_URL=postgresql://amnezia:amnezia@localhost:5432/amnezia_panel