fix(compression): exclude completion tokens from compression trigger (#12026)

Cherry-picked from PR #12481 by @Sanjays2402.

Reasoning models (GLM-5.1, QwQ, DeepSeek R1) inflate completion_tokens
with internal thinking tokens. The compression trigger summed
prompt_tokens + completion_tokens, causing premature compression at ~42%
actual context usage instead of the configured 50% threshold.

Now uses only prompt_tokens — completion tokens don't consume context
window space for the next API call.

- 3 new regression tests
- Added AUTHOR_MAP entry for @Sanjays2402

Closes #12026

run_agent.py

@@ -11736,10 +11736,12 @@ class AIAgent:
                     # should_compress(0) never fires.  (#2153)
                     _compressor = self.context_compressor
                     if _compressor.last_prompt_tokens > 0:
-                        _real_tokens = (
-                            _compressor.last_prompt_tokens
-                            + _compressor.last_completion_tokens
-                        )
+                        # Only use prompt_tokens — completion/reasoning
+                        # tokens don't consume context window space.
+                        # Thinking models (GLM-5.1, QwQ, DeepSeek R1)
+                        # inflate completion_tokens with reasoning,
+                        # causing premature compression.  (#12026)
+                        _real_tokens = _compressor.last_prompt_tokens
                     else:
                         _real_tokens = estimate_messages_tokens_rough(messages)