feat(matrix): add SvelteKit Matrix client (Phase 1)

Implements a minimal self-hosted Matrix chat client with:
- matrix-js-sdk integration with Svelte 5 runes store
- Password login with homeserver discovery
- Room list (DMs and groups) with unread counts
- Message timeline with typing indicators
- Send messages with Enter key
- Responsive chat UI with Tailwind CSS

Project structure:
- apps/matrix/apps/web: SvelteKit client (port 5180)
- apps/matrix/packages/shared: Shared types

Commands: pnpm dev:matrix:web

https://claude.ai/code/session_01RUrt2qN1D3nVh9HcGpwoby

apps/matrix/packages/shared/package.json

@@ -0,0 +1,18 @@
+{
+	"name": "@matrix/shared",
+	"version": "0.1.0",
+	"private": true,
+	"type": "module",
+	"main": "./src/index.ts",
+	"types": "./src/index.ts",
+	"exports": {
+		".": "./src/index.ts",
+		"./types": "./src/types.ts"
+	},
+	"scripts": {
+		"type-check": "tsc --noEmit"
+	},
+	"devDependencies": {
+		"typescript": "^5.8.3"
+	}
+}