feat: self-improving skills — agent-proposed updates with diff review, version history, and rollback (#355)

[MatthewSuttles]

Summary

Phase 5 of the Hermes-Inspired Agent Intelligence MEGAPLAN. Agents can now propose improvements to existing skills, admins review a side-by-side diff, and every content change is versioned with rollback capability.

• Skill update proposals: agents submit full updated content + rationale via propose_skill_update tool — no skill is modified until an admin approves
• Version history: every skill save (create, admin edit, agent update approval, rollback) is snapshotted in skill_versions with source attribution and proposal linkage
• Admin review UI: /skills/update_proposals lists pending proposals with side-by-side original/proposed diff, approve/reject actions with optional notes
• Rollback: /skills/:id/history shows the full version timeline; any prior version can be restored in one click (creates a new 'rollback' version so history stays linear)
• Unhelpful signals: agents call flag_skill_unhelpful to record that a skill didn't help, with a reason — visible improvement signal for admins

Deliverables

Data

• skill_versions table — immutable content snapshots
• skill_update_proposals table — pending/approved/rejected agent-submitted diffs
• flagged_reason + flagged_at columns on skill_load_events

Models

• SkillVersion with snapshot! class method
• SkillUpdateProposal with stale? detection (skill changed after proposal)
• Skill extended with has_many associations and auto-snapshot callbacks

Services

• Skills::UpdateProposer — validates + persists pending proposal
• Skills::UpdateApprover — applies content, creates attributed version, resolves ApprovalRequest
• Skills::UpdateRejector — closes proposal, resolves ApprovalRequest
• Skills::Rollback — restores content from target version, creates rollback version

Agent tools

• propose_skill_update executor + seed
• flag_skill_unhelpful executor + seed

Admin UI

• GET /skills/update_proposals — proposal list with diff view
• PATCH /skill_update_proposals/:id/approve_update_proposal
• PATCH /skill_update_proposals/:id/reject_update_proposal
• GET /skills/:id/history — version timeline with rollback buttons
• PATCH /skills/:id/rollback — restore to version

Specs

• 8 new service/executor specs
• 2 new model specs
• 3 new factories

Test plan

• Run bin/rspec spec/models/skill_version_spec.rb spec/models/skill_update_proposal_spec.rb
• Run bin/rspec spec/services/skills/update_proposer_spec.rb spec/services/skills/update_approver_spec.rb spec/services/skills/update_rejector_spec.rb spec/services/skills/rollback_spec.rb
• Run bin/rspec spec/services/tools/propose_skill_update_executor_spec.rb spec/services/tools/flag_skill_unhelpful_executor_spec.rb
• Verify bin/rails routes shows history/rollback/update_proposals/approve/reject routes
• Smoke test: create a skill, call propose_skill_update via agent, approve via admin UI, verify content changed and version history shows two entries
• Smoke test rollback: roll back to v1, verify content restored and v3 appears as 'rollback' type