chore(ci): replace mirror.yml with reusable wrapper

Pins to hyperpolymath/standards#187 merge SHA e6b2884722350515934d443daf23442f2195796f. Replaces the
canonical mirror.yml (~145 lines, drift-prone) with a thin ~13-line
wrapper. Forge selection still externalised to vars.<FORGE>_MIRROR_ENABLED.

Part of estate-wide convergence campaign 2026-05-26
(standards#199 / #187).

Author: hyperpolymath

.github/workflows/mirror.yml

@@ -1,36 +1,15 @@
 # SPDX-License-Identifier: MPL-2.0
-name: Mirror to GitLab and Bitbucket
+name: Mirror to Git Forges
 
 on:
   push:
-    branches: [ main ]
+    branches: [main]
+  workflow_dispatch:
 
 permissions:
   contents: read
 
 jobs:
   mirror:
-    name: Mirror repositories
-    runs-on: ubuntu-latest
-    if: github.repository == 'hyperpolymath/panic-attack'
-    steps:
-      - name: Checkout code
-        uses: actions/checkout@93cb6efe18208431cddfb8368fd83d5badbf9bfd # v5
-        with:
-          fetch-depth: 0
-
-      - name: Mirror to GitLab
-        if: vars.GITLAB_MIRROR_ENABLED == 'true'
-        env:
-          GITLAB_TOKEN: ${{ secrets.GITLAB_MIRROR_TOKEN }}
-        run: |
-          echo "Mirroring to GitLab..."
-          # git push --mirror https://oauth2:${GITLAB_TOKEN}@gitlab.com/hyperpolymath/panic-attack.git
-
-      - name: Mirror to Bitbucket
-        if: vars.BITBUCKET_MIRROR_ENABLED == 'true'
-        env:
-          BITBUCKET_TOKEN: ${{ secrets.BITBUCKET_MIRROR_TOKEN }}
-        run: |
-          echo "Mirroring to Bitbucket..."
-          # git push --mirror https://x-token-auth:${BITBUCKET_TOKEN}@bitbucket.org/hyperpolymath/panic-attack.git
+    uses: hyperpolymath/standards/.github/workflows/mirror-reusable.yml@e6b2884722350515934d443daf23442f2195796f
+    secrets: inherit