feat: DX, extensibility, and adaptive intelligence — completes 25-feature backlog

Sprint 5 — Developer Experience (D1-D5):
- Progress indicators with emoji phase markers during orchestration
- Dry-run mode: preview workflow without executing
- /archeflow:status and /archeflow:history commands
- Onboarding skill for first-time users

Sprint 6 — Extensibility (E1-E4, A4-A6):
- Archetype composition: combine 2 archetypes into super-reviewer
- Team presets: save common team configs in .archeflow/teams/
- Hook points: pre-plan, post-check, pre-merge, post-merge custom validation
- Workflow template library: api-design, migration, dep-upgrade, docs, hotfix
- Reviewer profiles: per-project config of which reviewers run
- Explorer cache: skip redundant research on recently-explored code
- Learning from history: track archetype usefulness, recommend profile changes

skills/onboarding/SKILL.md

@@ -0,0 +1,46 @@
+---
+name: onboarding
+description: Use when a user is new to ArcheFlow or asks "what is this?" / "how does this work?". Explains the plugin in 60 seconds.
+---
+
+# Welcome to ArcheFlow
+
+ArcheFlow is a Claude Code plugin that automatically coordinates multiple AI agents when you give implementation tasks. Instead of one agent doing everything, specialized agents with different perspectives collaborate through quality cycles.
+
+## What Just Happened
+
+When you installed ArcheFlow, it activated automatically. From now on:
+
+- **Give an implementation task** (feature, refactor, bug fix) → ArcheFlow kicks in
+- **Give a quick task** (typo fix, question, config edit) → Claude handles it normally
+
+You don't need to do anything different. Just describe your task.
+
+## The 30-Second Version
+
+```
+You: "Add user authentication with JWT"
+
+ArcheFlow:
+  🔍 Explorer researches your codebase (what files, what patterns, what tests)
+  <20><>️ Creator designs a proposal (architecture, file changes, test strategy)
+  ⚒️ Maker implements it in a safe branch (isolated, nothing breaks)
+  🛡️ Guardian reviews for security (injection, auth bypass, data exposure)
+  🤔 Skeptic challenges assumptions (what if JWT isn't the right choice?)
+  📚 Sage checks quality (readable? tested? consistent with codebase?)
+  ✅ All approve → merged. Issues? → automatic revision cycle.
+```
+
+## Key Concepts
+
+- **Archetypes:** 7 specialized agent roles, each with a unique perspective
+- **PDCA Cycles:** Plan → Do → Check → Act. If reviewers reject, it cycles back and improves
+- **Worktrees:** Code changes happen on isolated branches. Nothing touches main until approved.
+- **Shadow Detection:** If an agent gets stuck or dysfunctional, ArcheFlow detects and corrects it
+- **Workflows:** `fast` (1 cycle, quick fixes), `standard` (2 cycles, features), `thorough` (3 cycles, security)
+
+## Want to Learn More?
+
+- `/archeflow:orchestration` — See the full step-by-step execution guide
+- `/archeflow:shadow-detection` — How dysfunction is detected and corrected
+- `/archeflow:autonomous-mode` — Run tasks overnight unattended