Extract aliased project mutation primitive

[zwick]

Summary

Adds the package-local aliased GraphQL mutation primitive used by #2903, isolated from batch orchestration.

Why

This draft is stacked on #2922 so the batch implementation can be reviewed as a linear set of focused changes.

What changed

• Build and cache bounded positional reflected mutation types for update and clear operations.
• Execute mutations through the existing githubv4.Client, preserving partial-data outcomes and testing GraphQL error classification directly.

MCP impact

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

Prompts tested (tool changes only)

• N/A

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

Adds an internal GraphQL primitive for bounded, aliased project-item mutations while preserving partial results.

Changes:

• Builds and caches reflected update/clear mutation types.
• Executes up to 20 aliased mutations and classifies GraphQL errors.
• Adds focused mutation construction and execution tests.

Show a summary per file

File	Description
pkg/github/projects_batch_mutation.go	Implements aliased mutation construction and execution.
pkg/github/projects_batch_mutation_test.go	Tests caching, aliases, limits, and error classification.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 1
• Review effort level: Medium