feat(skills): rename shortcuts skill and auto-enable caveman/ponytail on install

Rename the portable conversation-shortcut skill from agent-shortcuts to
shortcuts and re-prefix every token to soc* (sobu, soco, socobu, socon,
sona, sote) so each token mirrors its command and never places two
consonants next to each other. make install and make project now also
register the caveman and ponytail marketplaces and enable both plugins in
the target's .claude/settings.json so their SessionStart hooks activate
every session; the merge is non-destructive, idempotent, and leaves an
unparseable settings.json untouched.

- skills/shortcuts/SKILL.md: new name and soc* token table
- tests/test_shortcuts.py: assert present, sorted, soc-prefixed, no cluster
- remove skills/agent-shortcuts and tests/test_agent_shortcuts.py
- scripts/enable-plugins.js: node JSON merge helper
- scripts/install.sh: run the helper after copying skills
- README.md: document the auto-enable behavior

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

skills/shortcuts/SKILL.md

@@ -0,0 +1,19 @@
+---
+name: shortcuts
+description: >
+  Portable operator conversation shortcuts, reusable across every project.
+  Trigger when the user's message is exactly one of these tokens (optionally
+  followed by arguments): sobu, soco, socobu, socon, sona, sote. Expand the
+  shortcut to the listed meaning and act on the expanded instruction.
+---
+
+When an operator message is one of the shortcuts below, expand it to the meaning and act on it.
+
+| Shortcut | Meaning |
+| --- | --- |
+| `sobu` | Stage next bundle: stage the next logical bundle of verified changes, explain what it does, and list what still remains uncommitted. |
+| `soco` | Commit: commit the currently staged changes (pre-commit hooks run). |
+| `socobu` | Commit no-verify, then stage next bundle: run `socon` followed by `sobu`. |
+| `socon` | Commit no-verify: commit the currently staged changes with `--no-verify`. |
+| `sona` | New alias: add the shortcut the operator states to the appropriate table, keeping it sorted. |
+| `sote` | Run `make test`. |