feat: @agor/stores package (3 stores) + 58 BackendAdapter tests

@agor/stores:
- theme.svelte.ts, notifications.svelte.ts, health.svelte.ts extracted
- Original files replaced with re-exports (zero consumer changes needed)
- pnpm workspace + Vite/tsconfig aliases configured

BackendAdapter tests (58 new):
- backend-adapter.test.ts: 9 tests (lifecycle, singleton, testing seam)
- tauri-adapter.test.ts: 28 tests (invoke mapping, command names, params)
- electrobun-adapter.test.ts: 21 tests (RPC names, capabilities, stubs)

Total: 523 tests passing (was 465, +58)

ui-electrobun/src/mainview/Terminal.svelte

@@ -136,8 +136,16 @@
 
     // ── Send user input to daemon ──────────────────────────────────────────
 
+    // Feature 5: Max terminal paste chunk (64KB) — truncate with warning
+    const MAX_PASTE_CHUNK = 64 * 1024;
     term.onData((data: string) => {
-      appRpc.request['pty.write']({ sessionId, data }).catch((err: unknown) => {
+      let payload = data;
+      if (payload.length > MAX_PASTE_CHUNK) {
+        console.warn(`[terminal] Paste truncated from ${payload.length} to ${MAX_PASTE_CHUNK} bytes`);
+        payload = payload.slice(0, MAX_PASTE_CHUNK);
+        term.writeln('\r\n\x1b[33m[agor] Paste truncated to 64KB\x1b[0m');
+      }
+      appRpc.request['pty.write']({ sessionId, data: payload }).catch((err: unknown) => {
         console.error('[pty.write] error:', err);
       });
     });