[Enhancement]: Align .env.example with env vars actually used in src/ and reduce inconsistent env-var fallbacks #155
Description
Description
After scanning only src/**/*.py:
env keys referenced in src/: 132
env keys declared in .env.example: 115
env keys referenced in src/ but missing from .env.example: 45
This includes cases where multiple env keys represent the same concept (e.g. OpenAI base URL), and cases where code uses provider-specific keys that are not documented in .env.example.
Why this matters？
Unpredictable configuration source: effective values may come from a mix of passed config, env fallbacks, and defaults.
Debugging pain: users follow .env.example but still hit different code paths using undocumented env vars.
Maintenance cost: inconsistent naming (“_BASE_URL” variations) encourages more ad-hoc fallbacks.