Route get_merge_request_conflicts through alias

What does this MR do and why?

Routes the standalone get_merge_request_conflicts tool through get_merge_request as an alias, following the same pattern as get_job_log → get_job. When invoked as get_merge_request_conflicts, the service implicitly injects include: ['conflicts'], so callers get the same data without a separate tool.

This removes ~120 lines of duplicated CustomService code and consolidates conflict fetching into the GraphQL-backed facet added in !249457 (merged).

References

• Deprecate and remove MCP tools superseded by th... (#622712 - closed)
• Parent issue: #605878 (closed)
• Stacked on: !249457 (merged) (conflicts facet)
• Prior MR: !249456 (merged) (GraphQL conflictFiles field)
• Follow-up: #629462 (diff exclusion misses files renamed out of an excluded path)

Screenshots or screen recordings

How to set up and validate locally

Verified end to end on a local GDK running this branch, over the MCP JSON-RPC endpoint and again through Duo Chat.

1. Start GDK with the MCP server enabled, and create an OAuth token with the mcp scope
2. Call tools/list — get_merge_request is listed and get_merge_request_conflicts is not, because aliases stay hidden
3. Call tools/call with get_merge_request_conflicts against a merge request that cannot be merged — returns conflictFiles with raw Git conflict markers, plus conflictStatus: HAS_CONFLICTS
4. Make the same call with get_merge_request and include: ['conflicts'] — the payload is identical
5. Repeat step 3 as a user with only Reporter access to the source project — conflictFiles is null and conflictStatus is NO_PUSH_ACCESS, with isError: false
6. Repeat step 3 against a mergeable merge request — conflictStatus is NO_CONFLICTS, with isError: false
7. In Duo Chat, ask for get_merge_request_conflicts on a conflicted merge request — Duo resolves the alias and reports the conflicting files

Results from the local run

Check	Result
tools/list hides the alias	42 tools advertised, get_merge_request_conflicts absent
Old name still returns conflict content	2 files, HAS_CONFLICTS, all three marker types present
Alias vs include: ['conflicts']	payloads identical
Caller without push access	conflictFiles: null, conflictStatus: NO_PUSH_ACCESS, isError: false
Mergeable merge request	conflictStatus: NO_CONFLICTS, isError: false
Caller-supplied include	unioned with the alias facet rather than overwritten
Duo Chat	called gitlab_get_merge_request with include: ["conflicts"], one action, HAS_CONFLICTS

Duo Chat was exercised against gitlab-org/gitlab-test!9, which conflicts on files/ruby/feature.rb.

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