feat(models): add max context window for gpt-5.3-chat model (qodo-ai#2280)

Co-authored-by: Loc Nguyen <elliotnguyen968@gmail.com>

Author: ElliotNguyen68

pr_agent/algo/__init__.py

@@ -42,6 +42,7 @@
     'gpt-5.2-chat-latest': 128000,  # 128K, but may be limited by config.max_model_tokens
     'gpt-5.2-codex': 400000,  # 400K, but may be limited by config.max_model_tokens
     'gpt-5.3-codex': 400000,  # 400K, but may be limited by config.max_model_tokens
+    'gpt-5.3-chat': 128000,  # 128K, but may be limited by config.max_model_tokens
     'gpt-5.4': 272000,  # 272K safe default without opt-in 1M context parameters
     'gpt-5.4-2026-03-05': 272000,  # 272K safe default without opt-in 1M context parameters
     'gpt-5.4-mini': 400000,  # 400K, but may be limited by config.max_model_tokens