chore: README housekeeping and remove stale TODO

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tradingagents/llm_clients/TODO.md

@@ -1,15 +0,0 @@
-# LLM Clients - Consistency Improvements
-
-## Issues to Fix
-
-### 1. `validate_model()` is never called
-- Add validation call in `get_llm()` with warning (not error) for unknown models
-
-### 2. ~~Inconsistent parameter handling~~ (Fixed)
-- GoogleClient now accepts unified `api_key` and maps it to `google_api_key`
-
-### 3. ~~`base_url` accepted but ignored~~ (Fixed)
-- All clients now pass `base_url` to their respective LLM constructors
-
-### 4. ~~Update validators.py with models from CLI~~ (Fixed)
-- Synced in v0.2.2