Finish Phase 6: Push frontend, WebAuthn frontend, OpenAPI/Swagger

Frontend:
- stores/push.ts: fixed VAPID key endpoint, added checkSubscription, proper subscription format
- UserSettings.tsx: added [ENABLE PUSH] toggle and [REGISTER PASSKEY] button
- LoginForm.tsx: added [SIGN IN WITH PASSKEY] button

Backend:
- cmd/server/main.go: added Swagger annotations, /docs/* route
- docs/: generated swagger.json, swagger.yaml, docs.go
- Makefile: added docs target for swag init

docs/swagger.json

@@ -0,0 +1,23 @@
+{
+    "schemes": [
+        "http",
+        "https"
+    ],
+    "swagger": "2.0",
+    "info": {
+        "description": "A chaotic, self-hosted Discord-like platform API",
+        "title": "Dumpster API",
+        "contact": {},
+        "version": "1.0"
+    },
+    "host": "localhost:8080",
+    "basePath": "/api/v1",
+    "paths": {},
+    "securityDefinitions": {
+        "SessionAuth": {
+            "type": "apiKey",
+            "name": "dumpster_session",
+            "in": "cookie"
+        }
+    }
+}