chore: remove unused github.com/fatih/color

[alexandear]

Summary

Remove the github.com/fatih/color dependency by running go mod tidy.

Why

Because github.com/fatih/color is unused.

What changed

• Removed github.com/fatih/color and reflowed indirect deps after tidying in go.mod.
• Pruned obsolete color-related checksums from go.sum:1-120.
• Swapped CI dependency step to run go mod tidy -diff in go.yml.

MCP impact

• No tool or API changes
• Tool schema or behavior changed
• New tool added

Prompts tested (tool changes only)

• n/a (no tool changes)

Security / limits

• No security or limits impact
• Auth / permissions considered
• Data exposure, filtering, or token/size limits considered

Tool renaming

• I am renaming tools as part of this PR (e.g. a part of a consolidation effort)
  • I have added the new tool aliases in deprecated_tool_aliases.go
• I am not renaming tools as part of this PR

Lint & tests

• Linted locally with ./script/lint
• [] Tested locally with ./script/test

Docs

• Not needed
• Updated (README / docs / examples)

[Copilot]

Pull request overview

This PR removes the unused github.com/fatih/color dependency and improves CI validation by enforcing clean module files.

Changes:

• Removed unused github.com/fatih/color dependency and its transitive dependencies (mattn/go-colorable, mattn/go-isatty)
• Updated CI workflow to validate module file cleanliness with go mod tidy -diff instead of just downloading dependencies

Reviewed changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated no comments.

File	Description
go.mod	Removed github.com/fatih/color from require block and reflowed indirect dependencies alphabetically
go.sum	Removed checksums for fatih/color, mattn/go-colorable, mattn/go-isatty, and related golang.org/x/sys entries
.github/workflows/go.yml	Changed CI step from go mod download to go mod tidy -diff to enforce module file discipline