fix(pi): prevent duplicate Bigpowers slash commands

[jagged-teeth]

Summary

• keep generated .pi/prompts as the sole Bigpowers slash-command provider
• remove duplicate per-skill registerCommand() calls from omp-hooks
• retain native Pi skills, the bigpowers_skill tool, session notification, and Git safety hooks
• add regression coverage that rejects extension command registration while requiring the canonical prompt manifest
• reconcile the e82 specification, contributor docs, and generated bug registry artifacts

Why this approach

Prompt templates were Bigpowers' established and documented Pi slash-command mechanism before the OMP extension was added in v2.88.1. Removing extension command registration fixes the regression without removing an existing Pi package surface or making slash commands depend on extension execution.

Closes #121.

Verification

• node scripts/omp-smoke.ts
• bash scripts/validate-omp-extension.sh
• bash -n scripts/validate-omp-extension.sh
• bash scripts/validate-specs-yaml.sh
• git diff --check
• npm run compliance && bash scripts/run-verification-gates.sh && bash scripts/sync-skills.sh && bash scripts/trace-stories.sh --strict
  • deterministic golden suite: 40/40 passed
• fresh independent review: PASS, no findings

[danielvm-git]

Superseded by upstream merge in #124 — same fix approach. Thanks!

[danielvm-git]

Closing in favor of merged upstream fix #124. Same approach — thank you @jagged-teeth!