feat: add plan-aware Phase 1 workflow

[ducdmdev]

Summary

• Phase 1 now detects existing plan files, creates plans via writing-plans skill when none exist, audits all plans through a 7-check gate, and derives team decomposition from the approved plan
• Adds Early Exit for trivial tasks and Budget Constraints to keep Phase 1a lightweight
• Adds Plan Status Update step in Phase 5 to mark plans as COMPLETED/PARTIAL/ABANDONED after team finishes
• All 5 archetype skills updated with Phase 1a/1b references and Phase 5 Plan Status Update

Design

• Spec: docs/specs/2026-03-17-plan-aware-phase1-design.md
• Plan: docs/plans/2026-03-17-plan-aware-phase1.md
• 5-phase contract preserved — Phase 1 expands into 1a (plan detection) + 1b (decomposition)
• Plan-awareness logic lives in shared-phases.md, inherited by all archetypes

Files changed (10)

• docs/shared-phases.md — Core Phase 1a, 1b, Phase 2 template, Phase 5 plan status
• docs/workspace-templates.md — Plan File Conventions, updated Phase Checklist
• docs/team-archetypes.md — Plan-aware detection note
• skills/agent-{team,implement,research,audit,plan}/SKILL.md — Phase 1 + Phase 5 overrides
• README.md — Updated How It Works

Test plan

• Full test suite: 97/98 pass (1 pre-existing claude plugin validate CLI issue)
• Doc reference tests: all cross-references resolve (0 missing)
• Structural audit: 15/15 checks pass (cross-refs, step numbering, content consistency)
• Dry-run: plan scan with existing plans — correctly finds matching plan, filters COMPLETED plans, all 7 audit checks pass, User Decision Gate presents clean result
• Dry-run: no plan found path — correctly falls through to plan creation, context gathering works, writing-plans invocation unambiguous, fallback path traced
• Dry-run: Phase 5 status update — correctly follows archetype → shared reference chain, produces correct status string COMPLETED — Implemented via team {name} (YYYY-MM-DD)
• 5 issues found during dry-run testing — all fixed (fallback log timing, add-or-update wording, IN PROGRESS at Phase 3, root glob scope, date format)