fix(freebuff): derive commit summaries from git changes - #853

The prompt-string edits in run-terminal-command.ts and 02-intermediate-git-committer.ts are sensible, low-risk clarifications telling the agent to derive commit messages from git status/diff rather than the user's prompt. Those are fine as-is and easy to port.

The core of the PR, summarizeGitChangesForCommit in common/src/util/git-commit-summary.ts, is the problem. It's 175 lines of new logic plus 40 lines of tests, but nothing in this diff calls it — it's exercised only by its own test file. The PR description confirms this directly: "The exact cloud Git-tab route is not present in this public snapshot, so this PR places the fix in shared code... that cloud/private code can call or inherit." That means this doesn't actually fix the reported bug (prompt text showing up as commit titles in the cloud Git tab); it's a speculative function sitting in common/src/util/ waiting for something to call it, which nothing here does. The reported issue is almost certainly in the push/commit-summary path used by cloud, not in the agent's run_terminal_command git-commit flow this PR touches — those are two different mechanisms (one is an LLM writing a commit message via the tool prompt, the other is presumably a non-LLM summary generated at push time).

As it stands, a maintainer porting this would get dead code with no call site, plus two small prompt tweaks that may or may not be relevant to the actual bug. I'd split this: drop the unused helper/tests, or find the actual call site in the private repo and wire it in with a real integration point and test that exercises the actual bug path, not a synthetic one.