feat(gateway): opt-in cleanup of temporary progress bubbles (#21186)

When display.cleanup_progress (or display.platforms.<plat>.cleanup_progress)
is true, the gateway deletes tool-progress bubbles, long-running '⏳ Still
working...' notices, and status-callback messages after the final response
is delivered successfully. Currently effective on adapters that implement
delete_message (Telegram); silently no-ops elsewhere. Off by default.
Failed runs skip cleanup so bubbles stay as breadcrumbs.

Minimal plumbing: base.py's existing post_delivery_callback slot now chains
new registrations onto any existing callback (with per-callback exception
isolation) rather than clobbering. Stale-generation registrations are
rejected so they can't step on a fresher run's callbacks. This lets the
cleanup callback coexist with the background-review release hook already
registered on the same slot.

Co-authored-by: mrcharlesiv <Mrcharlesiv@gmail.com>

cli-config.yaml.example

@@ -875,6 +875,22 @@ display:
   # Toggle at runtime with /verbose in the CLI
   tool_progress: all
 
+  # Auto-cleanup of temporary progress bubbles after the final response lands.
+  # On platforms that support message deletion (currently Telegram), this
+  # removes the tool-progress bubble, "⏳ Still working..." notices, and
+  # context-pressure status messages once the final reply has been delivered —
+  # keeping long-running turns visible live, then tidy afterward. Failed runs
+  # leave the bubbles in place as breadcrumbs. Off by default.
+  # Per-platform override: display.platforms.telegram.cleanup_progress
+  #   true:  Delete tracked progress/status bubbles on successful turn
+  #   false: Leave everything in place (default)
+  # Example:
+  #   display:
+  #     platforms:
+  #       telegram:
+  #         cleanup_progress: true
+  cleanup_progress: false
+
   # Gateway-only natural mid-turn assistant updates.
   # When true, completed assistant status messages are sent as separate chat
   # messages. This is independent of tool_progress and gateway streaming.