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.

lib/profiles/design.profile

@@ -7,7 +7,8 @@
 # tooling, graphify) is bundled for convenience but never blocks. Keep these
 # lines in sync when adding/removing a core design tool.
 # GATE-BLOCK: frontend-design ui-ux-pro-max emil-design-eng design-html
-# GATE-BLOCK: design-motion-principles design-review design-consultation magic
+# GATE-BLOCK: design-motion-principles design-review design-consultation
+# GATE-BLOCK: 21st 21st-ui-build
 
 # Core design skills (gstack)
 design-shotgun
@@ -30,11 +31,19 @@ frontend-design                   external
 design-motion-principles          external
 impeccable                        external
 
+# External: 21st.dev pack — CLI-driven (no MCP, no API key). 21st-registry
+# and 21st-design-sync are publishing flows; installed but left parked.
+21st-ui-build                     external
+21st-ui-explore                   external
+21st-ui-review                    external
+21st-cli-use                      external
+21st-ai                           external
+
 # Plugin (auto-toggle)
 ui-ux-pro-max                     plugin@ui-ux-pro-max-skill
 
-# MCP — auto-toggle via lib/toggle-external.sh (needs MAGIC_API_KEY in .env)
-magic                             mcp
-
 # CLIs (advisory only — installed/not-installed)
+# 21st is NOT advisory: it is on the GATE-BLOCK list, so a missing CLI trips
+# the design gate. Install: npm i -g @21st-dev/cli  then  21st login
+21st                              cli
 graphify                          cli

lib/profiles/full.profile

@@ -86,9 +86,14 @@ ui-ux-pro-max                     plugin@ui-ux-pro-max-skill
 #   claude plugin enable pr-review-toolkit@claude-code-plugins
 # or profile-based: bash lib/profile.sh apply audit (audit.profile keeps it;
 # a later `set full` re-disables it — MANAGED_PLUGINS lifecycle).
-magic                             mcp
+21st-ui-build                     external
+21st-ui-explore                   external
+21st-ui-review                    external
+21st-cli-use                      external
+21st-ai                           external
 
 # === CLIs (advisory) =================================================
+21st                              cli
 ctx7                              cli
 graphify                          cli
 gsd                               cli

lib/profiles/web-full.profile

@@ -49,9 +49,14 @@ emil-design-eng                   external
 frontend-design                   external
 design-motion-principles          external
 impeccable                        external
+21st-ui-build                     external
+21st-ui-explore                   external
+21st-ui-review                    external
+21st-cli-use                      external
+21st-ai                           external
 ui-ux-pro-max                     plugin@ui-ux-pro-max-skill
-magic                             mcp
 
-# === CLIs (advisory) =================================================
+# === CLIs ============================================================
+21st                              cli
 ctx7                              cli
 graphify                          cli

lib/profiles/web.profile

@@ -38,11 +38,19 @@ frontend-design                   external
 design-motion-principles          external
 impeccable                        external
 
+# External: 21st.dev pack (publishing flows 21st-registry / -design-sync
+# stay parked)
+21st-ui-build                     external
+21st-ui-explore                   external
+21st-ui-review                    external
+21st-cli-use                      external
+21st-ai                           external
+
 # Plugin: UI/UX intelligence (auto-toggle)
 ui-ux-pro-max                     plugin@ui-ux-pro-max-skill
 
-# MCP: 21st-dev Magic component generator
-magic                             mcp
+# CLI: 21st.dev component catalog + UI generation (needs `21st login`)
+21st                              cli
 
 # CLI: ctx7 (doc lookup for fast-evolving libs like Next.js)
 ctx7                              cli