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/docs.go

@@ -0,0 +1,41 @@
+// Package docs Code generated by swaggo/swag. DO NOT EDIT
+package docs
+
+import "github.com/swaggo/swag"
+
+const docTemplate = `{
+    "schemes": {{ marshal .Schemes }},
+    "swagger": "2.0",
+    "info": {
+        "description": "{{escape .Description}}",
+        "title": "{{.Title}}",
+        "contact": {},
+        "version": "{{.Version}}"
+    },
+    "host": "{{.Host}}",
+    "basePath": "{{.BasePath}}",
+    "paths": {},
+    "securityDefinitions": {
+        "SessionAuth": {
+            "type": "apiKey",
+            "name": "dumpster_session",
+            "in": "cookie"
+        }
+    }
+}`
+
+// SwaggerInfo holds exported Swagger Info so clients can modify it
+var SwaggerInfo = &swag.Spec{
+	Version:          "1.0",
+	Host:             "localhost:8080",
+	BasePath:         "/api/v1",
+	Schemes:          []string{"http", "https"},
+	Title:            "Dumpster API",
+	Description:      "A chaotic, self-hosted Discord-like platform API",
+	InfoInstanceName: "swagger",
+	SwaggerTemplate:  docTemplate,
+}
+
+func init() {
+	swag.Register(SwaggerInfo.InstanceName(), SwaggerInfo)
+}