chore: fix duplicated java- prefix in shopping merchant directory names (#14468)

## Problem

Two modules were generated into directories with a duplicated `java-`
prefix:

- `java-java-shopping-merchant-issue-resolution`
- `java-java-shopping-merchant-order-tracking`

Every other module in this monorepo follows the `java-<service>`
convention, and all their sibling Merchant API libraries are named
`java-shopping-merchant-*` (accounts, conversions, datasources,
inventories, lfp, ...).

## Changes

- Renamed both directories to drop the extra `java-` prefix (done with
`git mv`, so history is preserved and the diff registers as pure
renames).
- Updated the `<module>` entries in the root `pom.xml`. They had been
sorted under `java-j*` (stranded between `java-iot` and `java-kms`) and
are now moved into their correct alphabetical position alongside the
other `java-shopping-merchant-*` modules.
- Fixed the GitHub `tree/main/...` links for both libraries in the root
`README.md`, which currently 404.
- Fixed `repo_short` in each module's `.repo-metadata.json`.

## Impact

None on published artifacts. Maven coordinates are unchanged — both
libraries already publish correctly as
`com.google.shopping:google-shopping-merchant-issue-resolution` and
`com.google.shopping:google-shopping-merchant-order-tracking`. This only
corrects directory naming and the stale links/metadata that referenced
it.

Author: blakeli0

README.md

@@ -8,7 +8,7 @@
   "transport": "grpc+rest",
   "language": "java",
   "repo": "googleapis/google-cloud-java",
-  "repo_short": "java-java-shopping-merchant-issue-resolution",
+  "repo_short": "java-shopping-merchant-issue-resolution",
   "distribution_name": "com.google.shopping:google-shopping-merchant-issue-resolution",
   "api_id": "merchantapi.googleapis.com",
   "library_type": "GAPIC_AUTO"