refactor: slim session-start hook from 55 to ~20 lines of injected context

Create ACTIVATION.md as minimal stub for session-start injection.
Full SKILL.md stays in place for on-demand loading when commands are invoked.

hooks/session-start

@@ -7,7 +7,7 @@ const path = require("path");
 
 try {
   const pluginRoot = path.resolve(__dirname, "..");
-  const skillFile = path.join(pluginRoot, "skills", "using-archeflow", "SKILL.md");
+  const skillFile = path.join(pluginRoot, "skills", "using-archeflow", "ACTIVATION.md");
 
   if (!fs.existsSync(skillFile)) {
     console.log("{}");

skills/using-archeflow/ACTIVATION.md

@@ -0,0 +1,22 @@
+# ArcheFlow -- Active
+
+Multi-agent orchestration using archetypal roles and PDCA quality cycles.
+
+## Session Start
+
+On activation, print ONE line then proceed silently:
+```
+archeflow v0.8.0 · 19 skills · <domain> domain
+```
+Domain: `writing` if `colette.yaml` exists, `research` if paper/thesis files, `code` otherwise.
+
+## When to Use
+
+| Need | Command |
+|------|---------|
+| Work the queue | `/af-sprint` |
+| Deep orchestration | `/af-run <task>` |
+| Code review | `/af-review` |
+| Simple fix / question | Skip ArcheFlow — just do it directly |
+
+Do NOT use ArcheFlow for: single-line fixes, questions, reading code, config tweaks, git ops.