Reuse TOKEN_FOR_GITEA for the wiki when TOKEN_FOR_GITEA_WIKI is absent

The Publish wiki workflow now reads secrets.TOKEN_FOR_GITEA_WIKI ||
secrets.TOKEN_FOR_GITEA, so the existing token can publish the wiki when it
has write:repository. Update the missing-token message, the credentials and
troubleshooting guides, the README, the tests and the affected English
wiki pages with their Danish and Bahasa Malaysia translations.

Task: MIL-005#8

guides/credentials.md

@@ -59,17 +59,19 @@ is ever printed.
 ## Wiki publishing secret
 
 The workflow **Publish wiki** (this repository only) copies `wiki/` to the Gitea
-wiki when a change to `wiki/` is merged to `main`. It uses its own secret so
-that the metadata sync tokens never get write access.
+wiki when a change to `wiki/` is merged to `main`. It uses `TOKEN_FOR_GITEA_WIKI`
+when that secret exists and otherwise reuses `TOKEN_FOR_GITEA`.
 
 | Secret | Content | Used for |
 | --- | --- | --- |
-| `TOKEN_FOR_GITEA_WIKI` | A bare token, a JSON string, or JSON with `GITEA_TOKEN` | Writing the wiki pages of this repository |
+| `TOKEN_FOR_GITEA_WIKI` (optional) | A bare token, a JSON string, or JSON with `GITEA_TOKEN` | Writing the wiki pages of this repository |
 
-- A Gitea personal access token with scope `write:repository`. Gitea has no
-  wiki-only scope, so create the token for a dedicated user that has write
-  access to this repository only. S05 approves the scope and S03 stores the
-  secret.
+- The token that is used needs scope `write:repository`, and its user needs
+  write access to this repository. Gitea has no wiki-only scope.
+- `TOKEN_FOR_GITEA` is documented above with `read:repository` only. Reusing it
+  for the wiki means raising its scope, which also gives the metadata sync
+  write access. A separate `TOKEN_FOR_GITEA_WIKI` for a dedicated user keeps
+  the sync token read-only. S05 decides which, and S03 stores the secret.
 - Calls made: `GET /repos/{owner}/{repo}`, `GET /repos/{owner}/{repo}/wiki/pages`,
   `GET`, `POST` and `PATCH /repos/{owner}/{repo}/wiki/...` and, for a page that
   no longer exists in `wiki/`, `DELETE /repos/{owner}/{repo}/wiki/page/{name}`.

guides/troubleshooting.md

@@ -30,7 +30,8 @@ never starts, or stops before the step) is a **runner** problem.
 | `TOKEN_FOR_GITEA must contain a non-empty GITEA_TOKEN.` | configuration | The JSON form needs a `GITEA_TOKEN` key |
 | `Could not determine the Gitea source repository.` | configuration | The run has no repository name; report as a defect |
 | `Expected at most one GitHub push mirror ... found N` | configuration | Keep one GitHub push mirror |
-| `TOKEN_FOR_GITEA_WIKI is missing or empty.` | configuration | Wiki publishing only: add the secret (see [credentials.md](credentials.md)) |
+| `No token for the wiki: set TOKEN_FOR_GITEA_WIKI, or TOKEN_FOR_GITEA.` | configuration | Wiki publishing only: add one of the secrets (see [credentials.md](credentials.md)) |
+| `... HTTP 403 ...` while publishing the wiki | permissions | Wiki publishing only: the token needs `write:repository` and write access to this repository |
 | `The wiki is not enabled on <repo>` | configuration | Wiki publishing only: enable the wiki in the repository settings |
 | `The wiki source directory ... has no Markdown pages` | configuration | Wiki publishing only: `wiki/` is empty or missing; nothing was changed |
 | `Could not determine the GitHub owner and repository ...` | configuration | The mirror address must look like `https://github.com/<owner>/<repo>.git` |