feat: add WannPassts booking app with Go backend and Vue frontend

Initial project setup for a privacy-focused, self-hosted scheduling app:

- Go backend with JWT auth, SQLite storage, and chi router
- Calendar integrations via Google OAuth (FreeBusy), CalDAV, and ICS links
- Public booking pages with configurable slots and booking requests
- AES-256-GCM encryption for stored provider tokens
- Vue 3 + TypeScript frontend with Vite, Pinia, and Vue Router
- Docs, .gitignore, and .env.example for local development

.gitignore

@@ -0,0 +1,45 @@
+# ─── Node / Frontend ────────────────────────────────────────────────
+node_modules/
+frontend/dist/
+frontend/node_modules/
+*.local
+npm-debug.log*
+.vite/
+
+# ─── Go / Backend ───────────────────────────────────────────────────
+backend/cmd/server/server
+backend/server
+backend/wannpassts-server
+*.exe
+*.exe~
+*.dll
+*.so
+*.dylib
+*.test
+*.out
+coverage.out
+
+# ─── SQLite-Datenbanken (Nutzerdaten!) ──────────────────────────────
+*.db
+*.db-wal
+*.db-shm
+
+# ─── Geheimnisse & Konfiguration ────────────────────────────────────
+# .env enthält Secrets – .env.example bleibt versioniert.
+.env
+.env.*
+!.env.example
+
+# ─── Editoren & Betriebssysteme ─────────────────────────────────────
+.idea/
+.vscode/
+*.swp
+*.swo
+*~
+.DS_Store
+Thumbs.db
+
+# ─── Sonstiges ──────────────────────────────────────────────────────
+logs/
+*.log
+tmp/