Add vision routing capacity statusline support

[imblucase]

Summary

• add request-local vision routing fixes and capability validation
• add model capacity metadata, context-window filtering, and max_tokens clamping before upstream calls
• add a redacted /statusline snapshot endpoint for local statusline integrations
• improve token counting consistency for tools, thinking blocks, and conservative image accounting
• add build info to health/startup paths and safer daemon process handling

Why

Claude Code can report a 1M context for its declared Anthropic model while oc-go-cc dynamically routes to OpenCode Go models with different context windows. The proxy needs to decide eligibility before streaming headers or upstream calls, and local statusline integrations need a safe source for the effective model/window.

Validation

• go test ./...
• go test -race ./...
• oc-go-cc-vision.exe validate with local config
• local smoke: over-context request returns 400 before upstream and /statusline reports skipped fallbacks