feat(gateway): expose subagent tool calls and thinking to user (fixes #169) (#186)

When subagents run via delegate_task, the user now sees real-time
progress instead of silence:

CLI: tree-view activity lines print above the delegation spinner
  🔀 Delegating: research quantum computing
     ├─ 💭 "I'll search for papers first..."
     ├─ 🔍 web_search  "quantum computing"
     ├─ 📖 read_file  "paper.pdf"
     └─ ⠹ working... (18.2s)

Gateway (Telegram/Discord): batched progress summaries sent every
5 tool calls to avoid message spam. Remaining tools flushed on
subagent completion.

Changes:
- agent/display.py: add KawaiiSpinner.print_above() to print
  status lines above an active spinner without disrupting animation.
  Uses captured stdout (self._out) so it works inside the child's
  redirect_stdout(devnull).

- tools/delegate_tool.py: add _build_child_progress_callback()
  that creates a per-child callback relaying tool calls and
  thinking events to the parent's spinner (CLI) or progress
  queue (gateway). Each child gets its own callback instance,
  so parallel subagents don't share state. Includes _flush()
  for gateway batch completion.

- run_agent.py: fire tool_progress_callback with '_thinking'
  event when the model produces text content. Guarded by
  _delegate_depth > 0 so only subagents fire this (prevents
  gateway spam from main agent). REASONING_SCRATCHPAD/think/
  reasoning XML tags are stripped before display.

Tests: 21 new tests covering print_above, callback builder,
thinking relay, SCRATCHPAD filtering, batching, flush, thread
isolation, delegate_depth guard, and prefix handling.

run_agent.py

@@ -3312,6 +3312,24 @@ class AIAgent:
                 # Handle assistant response
                 if assistant_message.content and not self.quiet_mode:
                     print(f"{self.log_prefix}🤖 Assistant: {assistant_message.content[:100]}{'...' if len(assistant_message.content) > 100 else ''}")
+
+                # Notify progress callback of model's thinking (used by subagent
+                # delegation to relay the child's reasoning to the parent display).
+                # Guard: only fire for subagents (_delegate_depth >= 1) to avoid
+                # spamming gateway platforms with the main agent's every thought.
+                if (assistant_message.content and self.tool_progress_callback
+                        and getattr(self, '_delegate_depth', 0) > 0):
+                    _think_text = assistant_message.content.strip()
+                    # Strip reasoning XML tags that shouldn't leak to parent display
+                    _think_text = re.sub(
+                        r'</?(?:REASONING_SCRATCHPAD|think|reasoning)>', '', _think_text
+                    ).strip()
+                    first_line = _think_text.split('\n')[0][:80] if _think_text else ""
+                    if first_line:
+                        try:
+                            self.tool_progress_callback("_thinking", first_line)
+                        except Exception:
+                            pass
                 
                 # Check for incomplete <REASONING_SCRATCHPAD> (opened but never closed)
                 # This means the model ran out of output tokens mid-reasoning — retry up to 2 times