Fix tracking_freshness TD severity dropout and table wrap-blindness

[Hidden-History]

Summary

• render_td_index enumerated only HIGH/MEDIUM/LOW plus a literal UNSPECIFIED bucket, so an open CRITICAL record was tallied into the Open count but never printed in the breakdown. Rewritten to use the same residual pattern as render_bugs_index: sum the known buckets and report the remainder as other/unspecified, so no severity value — including one not yet invented — can be silently dropped.
• _STATUS_TABLE_RE and _SEV_TABLE_RE only matched a table cell on a single line, so a hard-wrapped Status or Severity cell (e.g. TECH-DEBT-934) returned no match at all. Both regexes now tolerate a cell wrapped across lines, while refusing to cross into a line that opens a new table row, so a malformed cell missing its closing pipe still cannot swallow the next row.

Test plan

• tests/unit/test_tracking_freshness_skill.py — 184 passed, including 6 new tests (2 wrap-tolerance cases + 1 adjacent-row non-swallow guard for each of Status/Severity, plus 2 CRITICAL/residual breakdown cases for the TD writer)
• _ai-memory/pov/skills/aim-tracking-freshness/tests/test_tracking_freshness_integration.py — passed
• _ai-memory/pov/skills/aim-tracking-freshness/tests/test_decision_log_coverage.py — passed
• _ai-memory/pov/skills/aim-tracking-freshness/tests/test_verify_code_state.py — passed
• New tests observed red against the unmodified source before the fix, green after
• black, ruff, isort clean on both changed files