fix: hide write UI resources in read-only mode

[he-yufeng]

Summary

• pass the server read-only setting into MCP App UI resource registration
• keep the read-only get_me_ui resource available
• skip issue_write_ui and pr_write_ui when write tools are filtered by --read-only

Fixes#2519.

To verify

• go test ./pkg/github -run "TestRegisterUIResources_ReadOnlySkipsWriteResources|TestRegisterUIResources_ReadableViaClient|TestNewMCPServer_RegistersUIResources" -count=1
• go test ./pkg/github -count=1
• git diff --check

[he-yufeng]

Validated the current branch locally after closing the superseded #2574:

go test ./pkg/github -run UIResources
git diff --check origin/main...HEAD

[he-yufeng]

Rebased on current main in b8743ed.

Validation:

• go test ./pkg/github -run UIResources
• git diff --check origin/main...HEAD

[he-yufeng]

Rebased on current main and reran the targeted validation locally.

Validated:

gofmt -w $(git diff --name-only origin/main...HEAD |Where-Object { $_-like'*.go' })
go test ./pkg/github -run UIResources
go test ./pkg/github
git diff --check origin/main...HEAD

All passed after the rebase.

[he-yufeng]

Closing this older duplicate branch in favor of #2612, which carries the same read-only UI resources fix on the newer replacement branch. Keeping only #2612 avoids splitting review across two identical PRs.