docs: document wiki sync workflow

Author: OgeonX-Ai

docs/ci-cd/wiki-sync.md

@@ -0,0 +1,42 @@
+# Wiki Sync
+
+The GitHub Wiki is a separate git repository. Files under this repository's `wiki/` folder do not appear in the actual Wiki tab until they are pushed to the wiki repository.
+
+## Current solution
+
+This repo includes `.github/workflows/sync-wiki.yml`.
+
+Run it manually from GitHub Actions:
+
+1. Open Actions.
+2. Select `sync-wiki`.
+3. Click `Run workflow`.
+4. Check that the Wiki tab shows the pages.
+
+## If the default token cannot push
+
+Create a repository secret named `WIKI_TOKEN` with permission to write repository contents and wiki pages, then run the workflow again.
+
+## Wiki source
+
+Canonical wiki source files live in:
+
+```text
+wiki/
+```
+
+## Sync loop
+
+```mermaid
+flowchart TD
+    Edit[Edit repo wiki folder] --> Commit[Commit to main]
+    Commit --> Workflow[sync-wiki workflow]
+    Workflow --> Clone[Clone wiki git repo]
+    Clone --> Copy[Copy pages]
+    Copy --> Push[Push to actual GitHub Wiki]
+    Push --> Verify[Open Wiki tab]
+    Verify --> Done{Pages visible?}
+    Done -- No --> Token[Check token or WIKI_TOKEN]
+    Token --> Workflow
+    Done -- Yes --> Complete[Complete]
+```