fix(response_analyzer): progress detection in non-git multi-repo workspaces

[DrumRobot]

Summary

Fixes #340 — in a multi-repo workspace whose root folder is not a git repository, analyze_response could never see progress: the git rev-parse --git-dir gate failed every loop, file-change detection was skipped entirely, and the Claude CLI result JSON carries no files_modified field. Every loop counted as no-progress and the circuit breaker opened unconditionally after the threshold.

This PR adds three complementary signal paths (any one of them ends the false-positive class):

1. $RALPH_DIR repo fallback — new _resolve_git_progress_dir() helper prefers the CWD repository and falls back to the tracker directory's own repository. Tracker updates (fix_plan.md) become the progress proxy. The .loop_start_sha commit-range comparison stays CWD-repo-only, since the recorded SHA belongs to the CWD repository; fallback mode counts uncommitted changes only.
2. RALPH_STATUS self-report — parse_json_response() now extracts FILES_MODIFIED: <N> and PROGRESS: true from the RALPH_STATUS block embedded in the .result text, with the same explicit-intent semantics and the same start-of-line anchoring as the existing EXIT_SIGNAL extraction (prose mentions do not trigger). Structured metadata stays authoritative — the self-report fills the gap, never lowers the count.
3. JSON-path has_progress from files_modified — a structured or self-reported positive files_modified sets has_progress directly, instead of relying exclusively on git detection.

Scope note: the self-report extraction is implemented for the JSON path (.result field) only, matching the Claude CLI output format where the bug was observed. Text-mode outputs already benefit from path 1.

Test plan

• 5 new regression tests in tests/unit/test_exit_detection.bats (issue Circuit breaker false positive: progress detection is blind when the loop CWD is not a git repository (multi-repo workspace) #340 section):
  • tracker-repo fallback detects a modified fix_plan.md when the CWD is not a repo (fails on main, passes here)
  • no repo anywhere → completes cleanly with has_progress=false (no crash, no fabricated progress)
  • FILES_MODIFIED: 3 self-report → files_modified=3, has_progress=true (fails on main)
  • PROGRESS: true without a file count → has_progress=true, files_modified=0 (fails on main)
  • explicit FILES_MODIFIED: 0 → has_progress stays false
• Full test_exit_detection.bats suite: 72/72 pass
• test_json_parsing.bats: no failures (RALPH_STATUS anchoring tests unaffected)
• test_circuit_breaker_recovery.bats: no failures