feat(skills): add 3-way adversarial plan-challenge phase to reflection orchestrators

After a plan/reflection is elaborated and before it executes, three fresh blind
sub-agents (correctness / robustness / simplicity) attack it on the big model;
the main loop RE-THINKS every aspect a BLOCKER lands (a named plan change, or
[deferred]) and re-challenges once if the plan materially changed. Advisory into
each skill's existing human gate — the human stays the decider.

- lib/challenge-plan.md — reusable phase: fail-safe (never fail open),
  severity-driven (any single-lens BLOCKER = must-address), RE-THINK loop
- agents/plan-challenger.md — challenger role (read-only, big-model per BDR-066)
- lib/tests/plan-challenger.test.sh — 41-assertion structure lock
- wired into 11 orchestrators: ship-feature/init-project/feat/bugfix (build-plan),
  onboard/audit-delta/code-clean (proposals), seo/geo/harden/web-validate (fix-bundle)

Hardened by dogfooding: 3 blind challengers reviewed this feature's own v1 plan
and caught 4 BLOCKERs (fail-open, consensus-buries-lone-finding, wrong model
tier vs BDR-066, false on-disk-plan premise) — all fixed here.

skills/bugfix/SKILL.md

@@ -117,6 +117,19 @@ RISK: <low/medium — what could go wrong>
 - If the fix is significant (>10 lines, multiple files,
   behavior change): wait for user approval.
 
+## STEP 3b — CHALLENGE THE FIX PLAN (before the contract)
+Unless the fix is the trivial 1-2 line case STEP 3 already fast-paths, the
+DIAGNOSIS + FIX PLAN is a reflection worth attacking before it hardens into a
+contract. Persist it to `.claude/tasks/plans/<date>-<slug>-<HHMM>.md`, then run
+`$HOME/.claude/lib/challenge-plan.md` with `PLAN` = that file, `KIND` = `build-plan`,
+`SCOPE` = the FIX PLAN files, `CONSTRAINTS` = the STEP 2 in-force BDR/LRN/BLK
+dispositions. Three blind challengers attack it (correctness = is the root cause
+right; robustness = blast radius / regressions; simplicity = is the fix minimal);
+RE-THINK every aspect a BLOCKER lands, re-challenge once if the plan materially
+changed. STEP 3.5 writes the contract from the REVISED plan. Print a CHALLENGE SUMMARY
+(BLOCKERs addressed / deferred / lenses returned), folding any deferred BLOCKER into
+the STEP 3 approval gate.
+
 ## STEP 3.5 — CONTRACT
 
 Run `$HOME/.claude/lib/contract-interview.md` (main loop). The DIAGNOSIS