docs(bin): give every bin skill a README

The bin skills were the only plugin without per-skill READMEs, so a reader
had to open SKILL.md — an agent-facing contract, not an explainer — to learn
what a skill does and when it fires. Each README states purpose, triggers and
boundaries for a human audience, leaving SKILL.md free to stay terse.

plugins/bin/skills/caveman/README.md

@@ -0,0 +1,29 @@
+# caveman
+
+Ultra-compressed output mode: drop articles, filler and pleasantries, keep the technical substance exact.
+
+## What it does
+
+Switches the agent into a terse register — no articles, no hedging, no pleasantries, fragments allowed, arrows for causality — while leaving technical terms, code blocks and quoted error strings untouched. The mode is *sticky*: once turned on it stays on for every subsequent response until the user says "stop caveman" or "normal mode", rather than decaying back to normal prose after a few turns.
+
+It carries one built-in escape hatch. Security warnings, confirmations for irreversible actions, multi-step sequences where fragment order could be misread, and any request to clarify are answered in normal prose, then the compressed register resumes.
+
+## Hand-invoked only
+
+`SKILL.md` sets `disable-model-invocation: true`. This is the single most important thing to know about this skill: **the model cannot route to it.** No other skill can hand off to it, and no phrasing in a user's request will cause it to be selected automatically. The only way in is the human typing `/caveman`.
+
+That is deliberate — output style is the user's choice, not an inference the router should make on their behalf. It is also why the description reads as one plain human-facing sentence rather than carrying the trigger phrasing and boundary clause a routable skill needs.
+
+## Usage
+
+```text
+/caveman
+```
+
+Then keep working normally. To leave the mode, say "stop caveman" or "normal mode".
+
+## Files
+
+| File | Purpose |
+|------|---------|
+| `SKILL.md` | The whole skill — persistence rule, compression rules, worked examples, and the auto-clarity exception |