fix(bluebubbles): add inbound message debouncing to coalesce URL link previews

When users send iMessages containing URLs, BlueBubbles sends separate
webhook events for the text message and the URL balloon/link preview.
This caused Clawdbot to receive them as separate queued messages.

This fix adds inbound debouncing (following the pattern from WhatsApp/MS Teams):

- Uses the existing createInboundDebouncer utility from plugin-sdk
- Adds debounceMs config option to BlueBubblesAccountConfig (default: 500ms)
- Routes inbound messages through debouncer before processing
- Combines messages from same sender/chat within the debounce window
- Handles URLBalloonProvider messages by coalescing with preceding text
- Skips debouncing for messages with attachments or control commands

Config example:
  channels.bluebubbles.debounceMs: 500  # milliseconds (0 to disable)

Fixes inbound URL message splitting issue.

extensions/bluebubbles/src/monitor.test.ts

@@ -146,8 +146,14 @@ function createMockRuntime(): PluginRuntime {
         resolveRequireMention: mockResolveRequireMention as unknown as PluginRuntime["channel"]["groups"]["resolveRequireMention"],
       },
       debounce: {
-        createInboundDebouncer: vi.fn() as unknown as PluginRuntime["channel"]["debounce"]["createInboundDebouncer"],
-        resolveInboundDebounceMs: vi.fn() as unknown as PluginRuntime["channel"]["debounce"]["resolveInboundDebounceMs"],
+        // Create a pass-through debouncer that immediately calls onFlush
+        createInboundDebouncer: vi.fn((params: { onFlush: (items: unknown[]) => Promise<void> }) => ({
+          enqueue: async (item: unknown) => {
+            await params.onFlush([item]);
+          },
+          flushKey: vi.fn(),
+        })) as unknown as PluginRuntime["channel"]["debounce"]["createInboundDebouncer"],
+        resolveInboundDebounceMs: vi.fn(() => 0) as unknown as PluginRuntime["channel"]["debounce"]["resolveInboundDebounceMs"],
       },
       commands: {
         resolveCommandAuthorizedFromAuthorizers: mockResolveCommandAuthorizedFromAuthorizers as unknown as PluginRuntime["channel"]["commands"]["resolveCommandAuthorizedFromAuthorizers"],