feat(wiki): Phase 7 — active_lint_tracked + loop integration

[HydraOps-T-rav]

Summary

Closes the last gap from Phase 4: the RepoWikiLoop lint pass now writes to the tracked per-entry layout, producing the uncommitted diffs that _maybe_open_maintenance_pr turns into chore(wiki): maintenance PRs.

Before this PR, stale flagging only happened on the legacy gitignored store, so the Phase 4 PR-opening code path was dormant. With this PR, when a source issue closes, the loop writes status: stale into repo_wiki/{owner}/{repo}/{topic}/*.md and the next tick opens the maintenance PR.

Helpers in src/repo_wiki.py

• _split_tracked_entry(text) — forgiving frontmatter parser (no pydantic).
• _update_tracked_entry_status(text, *, status, stale_reason=None) — rewrites the status: line, optionally adds stale_reason.
• _tracked_entry_age_days(fields, now) — for the 90-day prune window.
• active_lint_tracked(tracked_root, repo_slug, closed_issues) — scans {tracked_root}/{repo_slug}/{topic}/*.md, flips active → stale with reason for closed source issues, prunes stale entries older than 90 days.

RepoWikiLoop._do_work

• Computes tracked_root = config.repo_root / config.repo_wiki_path when config.repo_wiki_git_backed is True.
• Merges tracked repos into the slug list before the no-repos early-return — a freshly migrated repo may only exist in the tracked location.
• After the legacy active_lint call, runs active_lint_tracked via asyncio.to_thread and folds its counters into stats.
• Module-level _list_tracked_repos gates on index.md / index.json (same as RepoWikiStore.list_repos).

What's out of scope

• compile_topic is still legacy-layout-only. Porting synthesis to the tracked layout is a follow-up; it requires emitting a new per-entry file and marking inputs as superseded, plus the WikiCompiler needs to read tracked entries.
• Admin-task execution still logs-only; tracked-layout mutations for force-compile / mark-stale / rebuild-index from the queue come next.

Tests (14 new, 78 total pass)

• tests/test_active_lint_tracked.py (12): zero-stats when missing/empty, flips active→stale, skips already-stale, ignores open + unknown source issues, prunes >90d, doesn't prune fresh stale, mark-then-not-prune in same pass, idempotence, malformed-frontmatter tolerance, counts across topics.
• tests/test_repo_wiki_loop_pr.py::TestTrackedActiveLintIntegration (2): end-to-end flip when source closed; opt-out when repo_wiki_git_backed=False.

Test plan

• uv run pytest tests/test_active_lint_tracked.py tests/test_repo_wiki_loop_pr.py tests/test_wiki_maint_queue.py tests/test_repo_wiki.py — 78 passed.
• make lint-check clean.
• CI make quality.
• After merge, the next wiki tick with a newly-closed issue produces a chore(wiki): maintenance YYYY-MM-DD PR in HydraFlow.

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