feat(matrix-manadeck-bot): add Matrix bot for card/deck management

- Full NestJS bot with matrix-bot-sdk integration
- Deck CRUD: list, create, view, delete decks
- Card management: view cards and card details
- AI generation: generate decks with AI (30 Mana)
- Study sessions: start learning sessions
- Progress tracking: due cards, statistics
- Public features: featured decks, leaderboard
- Credit system: mana balance display
- German/English command aliases
- Number-based reference system for decks and cards
- JWT auth via mana-core-auth
- Runs on port 3321

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

services/matrix-manadeck-bot/.env.example

@@ -0,0 +1,15 @@
+# Server
+PORT=3321
+
+# Matrix
+MATRIX_HOMESERVER_URL=http://localhost:8008
+MATRIX_ACCESS_TOKEN=syt_xxx
+MATRIX_ALLOWED_ROOMS=#manadeck:matrix.mana.how
+MATRIX_STORAGE_PATH=./data/bot-storage.json
+
+# ManaDeck Backend
+MANADECK_BACKEND_URL=http://localhost:3009
+MANADECK_API_PREFIX=/api
+
+# Mana Core Auth
+MANA_CORE_AUTH_URL=http://localhost:3001