Add statusline badge, hooks, and compress fixes

Add statusline support and installer/uninstaller hooks, improve compression tooling and docs. Key changes:

- Add caveman statusline badge script (hooks/caveman-statusline.sh) and wire it into install/uninstall (hooks/install.sh, hooks/uninstall.sh); installer now requires node, backs up settings.json, and makes the statusline executable.
- Enhance SessionStart hook (hooks/caveman-activate.js) to detect missing statusline config and emit a setup nudge; update hooks README with statusline usage and setup instructions.
- Add gemini-extension.json, AGENTS.md, and GEMINI.md to register skills and support Gemini CLI installation.
- Update README to mention statusline badge, Gemini CLI install, and agent list.
- Improve caveman-compress: rename skill (caveman-compress), clarify CLI path/usage in SKILL.md, return on validation failure without overwriting, bump benchmark encoding, and make compressor robust to LLM outer fences by stripping wrapping fences and expanding max_tokens; add explicit rule to avoid wrapping entire output in fences.
- Strengthen code-block extraction in validate.py to handle variable-length fences (```/~~~), nested fences, and CommonMark rules.
- Minor SKILL.md tweak: resume caveman mode when user asks to clarify or repeats question.

These changes integrate a visible status badge for Claude Code users, improve install/uninstall reliability, extend Gemini support, and make the compressor/validator more robust when interacting with LLM outputs.

GEMINI.md

@@ -0,0 +1,4 @@
+@./skills/caveman/SKILL.md
+@./skills/caveman-commit/SKILL.md
+@./skills/caveman-review/SKILL.md
+@./skills/compress/SKILL.md