chore: migrate from Yarn Classic to npm

Yarn Classic (1.x) is EOL. This repo now uses npm, matching the rest of
the CoreUI stack (both Angular repos already declare npm@11, the vanilla
and astro-docs repos are already on npm).

- lerna.json: npmClient yarn -> npm
- package.json: resolutions -> overrides; add packageManager npm@11.6.4
- CI: yarn install --ignore-engines -> npm ci (with npm cache)
- Commit package-lock.json (previously yarn.lock was gitignored, so every
  CI run and local release resolved the full tree fresh from npm with no
  review point). Remove the stale, never-committed packages/docs/yarn.lock.

Author: mrholek

.github/workflows/ci.yml

@@ -22,11 +22,10 @@ jobs:
       - uses: actions/setup-node@v4
         with:
           node-version: ${{ matrix.node-version }}
-      # yarn.lock is gitignored in this repo, so there is no lockfile to pin
-      # against or to key a cache on — install resolves from package.json.
-      - run: yarn install --ignore-engines
-      - run: yarn lib:build
-      - run: yarn lib:test
+          cache: npm
+      - run: npm ci
+      - run: npm run lib:build
+      - run: npm run lib:test
 
   lint:
     name: Lint
@@ -40,5 +39,6 @@ jobs:
       - uses: actions/setup-node@v4
         with:
           node-version: 22.x
-      - run: yarn install --ignore-engines
-      - run: yarn lint
+          cache: npm
+      - run: npm ci
+      - run: npm run lint

.gitignore

@@ -2,7 +2,6 @@
 coverage/
 dist/
 node_modules/
-yarn.lock
 
 # IDEs and editors
 .idea/

lerna.json

@@ -1,5 +1,5 @@
 {
-  "npmClient": "yarn",
+  "npmClient": "npm",
   "packages": ["packages/*"],
   "version": "5.12.0",
   "$schema": "node_modules/lerna/schemas/lerna-schema.json"