fix: resolve message submission and stuck processing bugs (#199)

## Summary

- **Fix `isProcessing` tracking**: The `isProcessing` store field was initialised as `false` and never set to `true` in production, making all submission guards no-ops. Now `setProcessing(true)` is called after `send_prompt` succeeds in both `handleSubmit` and `handleQuickAction`, and `setProcessingForConversation(id, false)` is called when the backend emits an idle/success/error state.
- **Fix auto-granted tools dropped on permission reconnect** (closes #198): `PermissionModal.svelte` was passing only session-granted tools when reconnecting after a permission approval, silently dropping `config.auto_granted_tools`. Fixed to merge both sets, matching the behaviour of every other `start_claude` call site.
- **Add mid-session watchdog**: A watchdog thread now kills the Claude Code process if a user message is sent but no `Result` arrives within 5 minutes. This triggers the existing disconnect/error flow so the user is notified and can reconnect. A generation counter ensures watchdogs from previous sessions exit cleanly when a new session starts.

## Test plan

- [ ] Send a message and verify the textarea is disabled and the stop button is visible while Claude is processing
- [ ] Verify the textarea re-enables after Claude finishes responding
- [ ] Enable a tool in default permissions (e.g. Read), start a session, trigger a permission approval for another tool, approve it — verify the previously auto-granted tool is no longer re-prompted
- [ ] Verify all existing tests pass (`./check-all.sh`)

✨ This PR was created with help from Hikari~ 🌸

Reviewed-on: #199
Co-authored-by: Hikari <hikari@nhcarrigan.com>
Co-committed-by: Hikari <hikari@nhcarrigan.com>

src/lib/stores/conversations.ts

@@ -560,6 +560,17 @@ function createConversationsStore() {
       });
     },
 
+    setProcessingForConversation: (conversationId: string, processing: boolean) => {
+      conversations.update((convs) => {
+        const conv = convs.get(conversationId);
+        if (conv) {
+          conv.isProcessing = processing;
+          conv.lastActivityAt = new Date();
+        }
+        return convs;
+      });
+    },
+
     addLine: (
       type: TerminalLine["type"],
       content: string,