chore(pr_validate): dedupe redundant bad-title patterns

Round 4 of self-validation surfaced one trivial NIT: `^update\.?$`
and `^updates?\.?$` are redundant — the `s?` form covers both.
Consolidate into the single inclusive pattern with an inline
comment so the intent is grep-able.

Round 4 verdict: PASS (1 nit, 0 blocking). Tiering converged in
4 rounds: 1→1→0 blocking findings across rounds 1/2/3/4. Without
tiering the same 4 rounds would have been 5/5/2/1 "failures" by
the old binary verdict — exactly the spiral PR #467 hit. Mission
accomplished.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: raullenchai

scripts/pr_validate/steps/cl_description_quality.py

@@ -57,12 +57,11 @@
     re.compile(r"^various\s+changes\.?$"),
     re.compile(r"^various\s+fixes\.?$"),
     re.compile(r"^tweaks?\.?$"),
-    re.compile(r"^update\.?$"),
+    re.compile(r"^updates?\.?$"),  # covers "update" and "updates"
     re.compile(r"^patch\.?$"),
     re.compile(r"^wip\.?$"),
     re.compile(r"^cleanup\.?$"),
     re.compile(r"^changes\.?$"),
-    re.compile(r"^updates?\.?$"),
     re.compile(r"^misc\.?$"),
     re.compile(r"^minor\s+(?:fix|change|update)\.?$"),
 )