docs(plugin): phase2/3 roadmap + plan updates (4/4)

[gh-xj]

📝 Description

Stacked series PR (4/4) for Plugin System Phase 2/3 docs alignment.

Scope in this PR:

• roadmap/design docs updated to match shipped contract
• speculative fields removed or marked deferred
• implementation parity notes added

🔗 Stack Context

• Expected merge chain: feat(plugin): phase2 core selection + resolver (1/4) #936 -> feat(agent): plugin bootstrap wiring + diagnostics (2/4) #937 -> feat(cli): plugin list + lint commands (3/4) #938 -> docs(plugin): phase2/3 roadmap + plan updates (4/4) #939
• Depends on feat(cli): plugin list + lint commands (3/4) #938
• This PR is part of a stack; incremental scope is relative to feat(cli): plugin list + lint commands (3/4) #938.
• Note: because the stack currently targets main, GitHub file view can include earlier stack commits.

📌 Implementation Parity Matrix

• plugin list documented as name + status only: cmd/picoclaw/internal/plugin/list.go
• Startup summary keys documented as shipped: cmd/picoclaw/internal/pluginruntime/bootstrap.go, cmd/picoclaw/internal/agent/helpers.go, cmd/picoclaw/internal/gateway/helpers.go
• Updated docs:
  • docs/plans/2026-02-28-plugin-system-phase2-phase3-design.md
  • docs/plans/2026-03-01-plugin-system-phase2-phase3-implementation.md
  • docs/plugin-system-roadmap.md

🗣️ Type of Change

• 🐞 Bug fix (non-breaking change which fixes an issue)
• ✨ New feature (non-breaking change which adds functionality)
• 📖 Documentation update
• ⚡ Code refactoring (no functional changes, no api changes)

🤖 AI Code Generation

• 🤖 Fully AI-generated (100% AI, 0% Human)
• 🛠️ Mostly AI-generated (AI draft, Human verified/modified)
• 👨‍💻 Mostly Human-written (Human lead, AI assisted or none)

🔗 Related Issue

Related: #473 (Plugin System Phase 2/3 rollout)
Depends on: #938

📚 Technical Context (Skip for Docs)

• Reference URL: feat(hooks/plugin): add lifecycle hooks + phase-1 plugin contract #473
• Reasoning: Ensure docs reflect shipped behavior exactly and reduce contract-drift risk during review.

🧪 Test Environment

• Hardware: N/A
• OS: N/A
• Model/Provider: N/A
• Channels: N/A

📸 Evidence (Optional)

Click to view Logs/Screenshots

• CI run: https://github.com/sipeed/picoclaw/actions/runs/22535574965
• Status: Linter ✅, Tests ✅

☑️ Checklist

• My code/docs follow the style of this project.
• I have performed a self-review of my own changes.
• I have updated the documentation accordingly.