Add get_parent method to issue_read

[zwick]

Summary

Add a get_parent method to the existing issue_read tool that reads an issue's parent — the upward counterpart to the existing get_sub_issues (children).

Why

issue_read could read an issue's children (get_sub_issues) but had no way to read its parent, even though the GitHub API exposes it. This fills that gap with a small, always-on method on a default tool.

Refs #2391, #950

What changed

• issue_read → new get_parent method. Reads the GraphQL Issue.parent field and returns a null parent when the issue isn't a sub-issue.
• Kept always-on (not feature-gated), mirroring get_sub_issues. The schema cost is one enum value plus a couple of doc lines.

MCP impact

• Tool schema or behavior changed — issue_read gains a get_parent method; existing methods are unchanged.

Prompts tested (tool changes only)

• "What's the parent of issue Issue: Fix incorrect VS Code installation URL (both buttons point to Insiders) #123 in owner/repo?" → issue_read / get_parent
• "Is issue Issue: Fix incorrect VS Code installation URL (both buttons point to Insiders) #123 a sub-issue of anything?" → get_parent (returns null parent when it isn't)

Security / limits

• Auth / permissions considered — read-only; requires repo scope like the rest of issue_read.

Tool renaming

• I am not renaming tools as part of this PR

Lint & tests

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

Docs

• Updated (README regenerated for the new issue_read method)

---

Split out from the original combined PR. The flag-gated issue dependency tools (issue_dependency_read / issue_dependency_write) now live in #2751.

[Copilot]

Pull request overview

Adds new feature-flagged MCP tools to read and modify GitHub Issue dependency relationships (blocked-by / blocking) using GraphQL connections and the addBlockedBy / removeBlockedBy mutations, filling a gap not covered by existing issue relationship tools.

Changes:

• Introduces issue_dependency_read (GraphQL Issue.blockedBy / Issue.blocking) with cursor pagination.
• Introduces issue_dependency_write (GraphQL addBlockedBy / removeBlockedBy) resolving issue numbers to node IDs in a single aliased query.
• Adds the issue_dependencies feature flag, tests, toolsnap snapshots, and regenerated docs sections.

Show a summary per file

File	Description
pkg/github/tools.go	Registers the new issue dependency tools in the overall tool inventory (feature-flag gated).
pkg/github/issue_dependencies.go	Implements read/write tools and supporting GraphQL query/mutation helpers.
pkg/github/issue_dependencies_test.go	Adds schema snapshot validation and behavior tests for the new tools.
pkg/github/feature_flags.go	Introduces the issue_dependencies flag and wires it into feature-flag sets.
pkg/github/toolsnaps/issue_dependency_read_ff_issue_dependencies.snap	Adds the flag-gated schema snapshot for the read tool.
pkg/github/toolsnaps/issue_dependency_write_ff_issue_dependencies.snap	Adds the flag-gated schema snapshot for the write tool.
docs/insiders-features.md	Documents the new issue_dependencies flag/tools in insiders features (generated section).
docs/feature-flags.md	Documents the new issue_dependencies flag/tools in feature flags (generated section).

Copilot's findings

• Files reviewed: 8/8 changed files
• Comments generated: 1