RFC: Environment variables should take precedence over config file in endpoint resolution

[5wxwxwxw5]

Problem

In v1.8.2, when both a provider config (~/.opencodereview/config.json) and environment variables (OCR_LLM_URL / OCR_LLM_TOKEN / OCR_LLM_MODEL) are set, the config file silently wins. In older versions, e.g. v1.3.1, env vars took precedence.

Root cause

internal/llm/resolver.go L71–79 defines the resolution order as:

1. OCR config file        ← currently wins
2. OCR environment vars
3. Claude Code environment
4. Shell rc file

Why this is a problem

• CI/CD: A stale config.json on a shared runner silently overrides the OCR_LLM_* env vars set by the pipeline — no warning, wrong model used, hard to debug.
• Convention: Nearly all CLI tools (aws, gh, docker) follow "env > config file". Users expect export OCR_LLM_MODEL=foo to override a file.

Proposal

Swap the first two strategies:

1. CLI flags (--model, --provider)       [already handled upstream]
2. OCR environment vars (OCR_LLM_*)     ← explicit runtime intent
3. OCR config file                       ← persistent default
4. Claude Code environment
5. Shell rc file

Additionally, emit a warning to stderr when both sources are present and one is ignored.