Fix: write trace domain snapshots even outside a git work tree

[collincunn]

Summary

postTraceMetrics writes the trace-level cc.<domain> blocks (skills, tools, memory, thinking, tool_results, user_prompts, file_attachments, prior_assistant, assistant_text) for every closing trace. It also writes a cc.git block when the current working directory is a git work tree. Today the function bails out entirely if cwd is not a git work tree, dropping all nine domain snapshots even though none of them touch git.

Repro

Launch Claude Code from a non-repo parent directory (e.g. `~/code` used as a holder for many sibling repos). Send any prompt with tracing enabled. The resulting Opik trace shows:

• ✅ `cc.identity` (written by `identity.applyToTrace` at trace creation)
• ✅ per-span `cc.llm_call` (written in the span loop)
• ❌ `cc.skills`, `cc.tools`, `cc.memory`, … (missing — `postTraceMetrics` returned at the git check)

Debug log signature: `postTraceMetrics: is not a git work tree`

Fix

Move the git work-tree check inline so it gates only the git block. Domain snapshots always run; the final PATCH is skipped only when both produced nothing.

Test plan

• Verified locally: ran CC from `/Users/collinc/code` (non-git), confirmed the closing trace now carries `cc.skills` and `cc.tools` alongside `cc.identity` — git block correctly absent
• `go vet ./src` clean
• Existing unit tests pass (`go test ./src/...`)
• Sanity-check inside a real repo to confirm git block still writes when available

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