task(ceremony): debug as mandatory discipline in implement fix-bug and verify

[pentaxis93]

Summary

Part of #191. Debug's Iron Law ("NO FIXES WITHOUT ROOT CAUSE INVESTIGATION FIRST") is contradicted by implement's conditional invocation ("If the root cause is unclear") and entirely absent from verify's failure handling.

Scope

File	Change
protocols/implement/PROTOCOL.md	Make debug invocation mandatory in fix-bug step 1
protocols/verify/PROTOCOL.md	Add investigation gate when verification reveals unexpected failure

Acceptance Criteria

• implement fix-bug procedure invokes debug unconditionally before any fix attempt — the conditional "if unclear" is removed because confident-but-wrong is the failure mode debug exists to prevent
• verify gate function includes an investigation step: when verification output shows unexpected failure, invoke debug to establish root cause before reporting status or retrying
• Cross-reference from verify to debug added
• Consistent with orient's integration principle (line 74): "do not guess. Investigate root cause before proposing any fix."

Dependencies

None — independent of the other tasks in #191.

Evidence

• implement/PROTOCOL.md line 224: "If the root cause is unclear, invoke debug first" — conditional contradicts debug's Iron Law
• verify/PROTOCOL.md lines 34-48: gate function has no investigation step for unexpected failures
• skills/debug/SKILL.md: "NO FIXES WITHOUT ROOT CAUSE INVESTIGATION FIRST" — no conditional
• orient/SKILL.md line 74: "do not guess. Investigate root cause before proposing any fix. debug provides the investigation methodology"