feat(21st): replace the magic MCP with the @21st-dev CLI + skill pack

Upstream supersedes `@21st-dev/magic` with `@21st-dev/cli` (bin `21st`):
same endpoint, `21st login` in place of an API key, no MCP process loaded
into every session.

- install-plugins.sh Step 8.7: `npm i -g @21st-dev/cli` (pinned in
  plugins.lock.json), staged `21st skills install`, TTY-only login offer,
  pack disabled by default. update-all.sh 7.4 refreshes both.
- The documented `21st install-skill` cannot be used: the installer refuses
  to follow a symlink on the target path and `~/.claude/skills` is one. The
  install runs under a throwaway HOME and the result moves into
  skills-external/21st-* (gitignored), symlinked on demand.
- toggle-external.sh manages `21st` as a pack (names globbed from
  skills-external/21st-*, parked under plain names). `magic` is gone.
- The 5 design skills join design/web/web-full/full and MANAGED_EXTERNALS;
  21st-registry and 21st-design-sync stay parked. MANAGED_MCPS is now empty
  and profile.sh's dead magic branches are removed.
- Design gate: GATE-BLOCK gains `21st` (required-manual, magic's old slot)
  and `21st-ui-build`; PATH repair extended to the npm global bin.
- settings.json: the 4 mcp__magic__* ask entries go; the outward-facing
  21st verbs land in autoMode.soft_deny, the tier that holds under auto
  mode (LRN-153).
- Docs: README, CLAUDE.global.md, design-gate.md, profile SKILL.md,
  .env.example, .gitleaks.toml, link.sh. BDR-093, LRN-158.

Tests: profile-set-managed 17/17, make test green except 2 pre-existing
gitflow FAILs (gitleaks binary absent on this host), shellcheck clean.

settings.json

@@ -235,11 +235,7 @@
       "WebFetch",
       "Bash(git stash pop*)",
       "Bash(git stash drop*)",
-      "Bash(git stash clear)",
-      "mcp__magic__21st_magic_component_builder",
-      "mcp__magic__21st_magic_component_refiner",
-      "mcp__magic__21st_magic_component_inspiration",
-      "mcp__magic__logo_search"
+      "Bash(git stash clear)"
     ],
     "defaultMode": "auto",
     "disableBypassPermissionsMode": "disable",
@@ -370,7 +366,8 @@
       "Moving or renaming a directory inside the repo (`mv src/api src/api_old`, or any `mv` of a tree). It breaks imports and paths silently, and the breakage surfaces far from the command. Clear only when the user asked for that move.",
       "An inline interpreter or `xargs` that deletes, or that writes outside the current working directory: `python3 -c`, `python -c` or `node -e` calling `rmtree`, `remove`, `unlink` or `truncate`; `xargs` feeding `rm`, `mv` or `dd`. `find ... | xargs rm` is the case that matters, since it routes around the `find * -exec rm` deny rule. Reading, computing, and editing a file inside the working directory pass untouched.",
       "Docker data destruction on this workstation: `docker rm -f`, `docker volume rm` or `prune`, `docker system prune`, `docker compose down -v` (drops named volumes, which hold local database data with no undo), and `docker run` with `--privileged` or a bind mount outside the current working directory. Clear only when the user named the container or volume in this turn.",
-      "Undeclared node packages: `npx <pkg>`, `pnpm dlx` or `yarn dlx` of a package absent from the manifest and lockfile runs code fetched at call time; `npm install <name>` or `pnpm add <name>` adds a dependency the house rule requires naming first. Clear only when the user named the package in this turn."
+      "Undeclared node packages: `npx <pkg>`, `pnpm dlx` or `yarn dlx` of a package absent from the manifest and lockfile runs code fetched at call time; `npm install <name>` or `pnpm add <name>` adds a dependency the house rule requires naming first. Clear only when the user named the package in this turn.",
+      "Publishing to the 21st.dev public catalog: `21st publish`, `publish-theme`, `publish-template`, `publish-gradient`, `publish-ascii`, `submit` and `resubmit` push a component, theme or template from this machine onto a public listing under the user's account; `21st edit`, `delete`, `withdraw`, `remove-from-catalog` and `21st profile set|upload` change or remove what is already published there. Retrieval and generation (`search`, `logo`, `get`, `add`, `generate`, `iterate`) are ordinary design work and pass. Clear only when the user asked to publish or change that specific item in this turn."
     ],
     "hard_deny": [
       "$defaults",