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/sync-landing-submodule.yml

@@ -1,29 +1,13 @@
-name: Sync landing docs submodule
-
+# 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:
-  push:
-    branches: [main]
   workflow_dispatch:
-
 permissions:
   contents: read
-
-concurrency:
-  group: sync-landing-docs-main
-  cancel-in-progress: false
-
 jobs:
-  sync:
-    if: github.repository == 'langbot-app/langbot-docs'
+  migrated:
+    if: ${{ false }}
     runs-on: ubuntu-latest
-    timeout-minutes: 5
     steps:
-      - uses: actions/checkout@v7
-        with:
-          persist-credentials: false
-      - name: Test synchronization contracts
-        run: python3 -m unittest discover -s tests -p test_sync_landing_submodule.py -v
-      - name: Update landing submodule and production fork
-        env:
-          GH_TOKEN: ${{ secrets.LANGBOT_WIKI_PUSH_TOKEN }}
-        run: python3 scripts/sync-landing-submodule.py
+      - run: echo 'Use the LangBot repository workflows.'