cli: make messages/ part of the configurable --pattern flag

Moves the messages/ path segment from being hardcoded into the export
and import commands to being part of the pattern itself. The default
pattern is now messages/{id}.{lang}.json, giving full control over the
directory structure under the translations output directory.

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>
Co-authored-by: Cursor <cursoragent@cursor.com>

docs/plugins/internationalization.md

@@ -382,7 +382,7 @@ const app = createApp({
 
 #### Custom file patterns
 
-By default, message files use the pattern `{id}.{lang}.json` (e.g. `catalog.en.json`). You can change this with the `--pattern` option:
+By default, message files use the pattern `messages/{id}.{lang}.json` (e.g. `messages/catalog.en.json`). You can change this with the `--pattern` option:
 
 ```bash
 yarn backstage-cli translations export --pattern '{lang}/{id}.json'
@@ -391,8 +391,8 @@ yarn backstage-cli translations export --pattern '{lang}/{id}.json'
 This produces a directory structure grouped by language instead:
 
 ```text
-translations/messages/en/catalog.json
-translations/messages/zh/catalog.json
+translations/en/catalog.json
+translations/zh/catalog.json
 ```
 
 The pattern is stored in the manifest, so the `import` command automatically uses the same layout.

docs/tooling/cli/03-commands.md

@@ -447,8 +447,9 @@ Usage: backstage-cli translations export [options]
 
 Options:
   --output <dir>       Output directory for exported messages and manifest (default: "translations")
-  --pattern <pattern>  File path pattern for message files, with {id} and {lang}
-                       placeholders (default: "{id}.{lang}.json")
+  --pattern <pattern>  File path pattern for message files relative to the output
+                       directory, with {id} and {lang} placeholders
+                       (default: "messages/{id}.{lang}.json")
   -h, --help           display help for command
 ```