fix: complete session reset — missing compressor counters + test

Follow-up to PR #2101 (InB4DevOps). Adds three missing context compressor
resets in reset_session_state():
- compression_count (displayed in status bar)
- last_total_tokens
- _context_probed (stale context-error flag)

Also fixes the test_cli_new_session.py prompt_toolkit mock (missing
auto_suggest stub) and adds a regression test for #2099 that verifies
all token counters and compressor state are zeroed on /new.

run_agent.py

@@ -1053,6 +1053,9 @@ class AIAgent:
         if hasattr(self, "context_compressor") and self.context_compressor:
             self.context_compressor.last_prompt_tokens = 0
             self.context_compressor.last_completion_tokens = 0
+            self.context_compressor.last_total_tokens = 0
+            self.context_compressor.compression_count = 0
+            self.context_compressor._context_probed = False
     
     @staticmethod
     def _safe_print(*args, **kwargs):