feat: fix slash commands, add badge UI, multi-provider management

Slash commands:
- Fix skills not appearing (removed non-existent `enabled` filter)
- Add badge/capsule UI for prompt-type commands (/compact, /review, etc.)
- SDK-native commands sent directly; CLI-only commands expanded to prompts
- /clear now resets SDK session and clears database messages
- /cost shows actual aggregated token usage statistics
- Keyboard: Backspace/Escape to remove badge, arrow keys auto-scroll popover
- Add /memory command for editing CLAUDE.md

Multi-provider management:
- CRUD API for API providers with SQLite storage
- ProviderManager UI with quick presets (GLM, Kimi, MiniMax, etc.)
- Dynamic model labels based on active provider
- Environment variable injection with conflict resolution

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

package.json

@@ -1,6 +1,6 @@
 {
   "name": "codepilot",
-  "version": "0.2.3",
+  "version": "0.3.0",
   "private": true,
   "main": "dist-electron/main.js",
   "scripts": {