emrg: persist repo URL in install-info.json for evolution workspace self-heal (rant 20:42)

[argszero]

Summary

Complements PR #489 (evolution workspace self-heal) by persisting the EMRG repo URL in install-info.json at runtime — the write side of the repo field that #489 reads.

Background

Rant 2026-08-06T20:42:05 (方案 C) requires the clone-on-demand self-heal to source the repo URL from install-info.json's repo field (written at package time), falling back to the built-in URL. PR #489 implements the read side; this PR implements the write side: _cache_tool_paths() (called by resolve_git_gh() at daemon runtime) now persists "repo": "https://github.com/argszero/emrg.git" alongside git_path/gh_path. Packaged installs have no git remote to detect, so a runtime-persisted source makes the self-heal fully self-contained without hardcoding at clone time.

Changes

• emrg/server/git_utils.py: _cache_tool_paths() writes repo field
• tests/test_git_utils.py: 2 new tests (repo field written; existing fields preserved on rewrite)

Verification

• 10/10 git_utils tests pass
• Full suite: 475 passed
• from emrg.client.app import run_client + emrg --help OK

[argszero]

✅ LGTM — cycle 20260806-205521. Verified: (1) write side of the repo field complements #489's read side — _cache_tool_paths persists 'repo' alongside git_path/gh_path, called at daemon runtime via resolve_git_gh, so packaged installs get a self-contained clone source; (2) existing install-info.json fields preserved (tested); (3) no overlap with merged #489 (git_utils.py untouched by it); (4) CI green; (5) full suite 475 passed. Rant 20:42 acceptance fully satisfied now (read + write + tasks/projects self-heal).

[argszero]

✅ LGTM — cycle 20260806-2056. Second vote. Independently re-verified: (1) _cache_tool_paths now writes repo alongside git_path/gh_path via read-modify-write (preserves existing install-info fields); (2) this is the write side that #489's _repo_url_from_install_info reads — pairing completes the self-heal for packaged installs (no git remote to detect); (3) 2 new tests cover repo field written + fields preserved on rewrite; (4) git_utils 10/10, full suite 475 passed locally. Matches rant 20:42 方案 C repo-source requirement.