feat: merge langbot-docs history into docs/ (subtree, no squash)

Imported langbot-app/langbot-docs main (51dddcb3f) under docs/ with
`git subtree add`, keeping every original commit SHA and signature so the
mirror and landing-page submodule can fast-forward from a `git subtree
split` later. Retarget the docs workflows to docs/, point blog sync at the
main repository, and update the remaining internal references.

Co-Authored-By: Mika (Multica) <[email protected]>
Co-authored-by: multica-agent <[email protected]>

docs/.github/workflows/tests.yml

@@ -1,28 +1,13 @@
-name: Tests
-
+# Workflows run from langbot-app/LangBot/.github/workflows after migration.
+# Keep this mirror entry inert: no job may write directly to langbot-docs.
+name: Legacy docs workflow (migrated)
 on:
-  pull_request:
   workflow_dispatch:
-
 permissions:
   contents: read
-
 jobs:
-  docs:
-    name: Fumapress docs build
+  migrated:
+    if: ${{ false }}
     runs-on: ubuntu-latest
-    timeout-minutes: 10
     steps:
-      - uses: actions/checkout@v7
-      - uses: actions/setup-node@v7
-        with:
-          node-version: "24"
-          cache: npm
-      - name: Install dependencies
-        run: npm ci
-      - name: Typecheck
-        run: npm run typecheck
-      - name: Run documentation contract tests
-        run: npm test
-      - name: Build and verify the static site
-        run: npm run build
+      - run: echo 'Use the LangBot repository workflows.'