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/components/PermissionModal.svelte

@@ -86,7 +86,7 @@
           api_key: config.api_key || null,
           custom_instructions: config.custom_instructions || null,
           mcp_servers_json: config.mcp_servers_json || null,
-          allowed_tools: newGrantedTools,
+          allowed_tools: [...new Set([...newGrantedTools, ...config.auto_granted_tools])],
           use_worktree: config.use_worktree ?? false,
           disable_1m_context: config.disable_1m_context ?? false,
         },