feat: add GitHub Issues Integration extension

[Fatima367]

Summary

Adds a community extension that generates spec artifacts from GitHub Issues, eliminating
duplicate work between issue tracking and Specification-Driven Development (SDD).

Resolves #2175

Problem

Developers already document requirements in GitHub Issues (user stories, acceptance criteria,
labels, discussions) but then rewrite everything from scratch in spec.md when starting SDD.
This creates:

• Duplicate work - Writing the same information twice
• Context loss - Losing valuable discussion and rationale from issues
• Sync drift - Issues and specs diverge over time
• Manual overhead - Copying and reformatting content manually

Solution

This extension provides three commands that bridge GitHub Issues and Spec Kit:

Commands

1. /speckit.github-issues.import - Import a GitHub Issue and generate structured spec.md - Fetches issue title, body, labels, and comments

   • Parses structured sections (problem, solution, alternatives)
   • Generates spec with requirements and acceptance criteria
   • Creates metadata for tracking

2. /speckit.github-issues.sync - Keep specs updated when source issues change

   • Detects changes in linked issues
   • Updates spec with latest issue data
   • Appends new comments to Discussion Notes
   • Maintains sync timestamps

3. /speckit.github-issues.link - Add bidirectional traceability

   • Links spec to source issue
   • Posts comment on GitHub Issue linking back to spec
   • Creates metadata file for tracking

Features

• ✅ Import GitHub Issues to structured spec.md files
• ✅ Structured parsing of problem statements, solutions, acceptance criteria
• ✅ Preserve valuable comments and context
• ✅ Bidirectional links between issues and specs
• ✅ Automatic sync when issues change
• ✅ Label integration as spec tags
• ✅ Issue state tracking (open/closed)

Extension Details

• Extension ID: github-issues
• Version: 1.0.0
• Category: integration
• Effect: Read+Write
• License: MIT
• Author: @Fatima367

Prerequisites

• GitHub CLI (gh) installed and authenticated
• Read access to target repositories
• Write access for bidirectional linking (optional)

Installation

After this PR is merged, users can install the extension from the main spec-kit repository:

# Install from local spec-kit directory
specify extension add --dev /path/to/spec-kit/spec-kit-github-issues

For testing this PR before merge:

# Clone the PR branch
git clone -b add-github-issues-extension https://github.com/Fatima367/spec-kit.git
cd spec-kit

# Install the extension
cd /path/to/your-project
specify extension add --dev /path/to/spec-kit/spec-kit-github-issues

## Testing

Tested locally with issue #2175:
- ✅ Successfully imported issue and generated spec.md
- ✅ Created proper metadata files
- ✅ Extension manifest validates correctly

##  Files Added:

- spec-kit-github-issues/extension.yml - Extension manifest
- spec-kit-github-issues/commands/import.md - Import command
- spec-kit-github-issues/commands/sync.md - Sync command
- spec-kit-github-issues/commands/link.md - Link command
- spec-kit-github-issues/README.md - Documentation
- spec-kit-github-issues/CHANGELOG.md - Version history
- spec-kit-github-issues/LICENSE - MIT License
- spec-kit-github-issues/github-issues-config.template.yml - Config template
- spec-kit-github-issues/.extensionignore - Ignore patterns

##  Checklist

- Valid extension.yml manifest
- Complete README with installation and usage instructions
- LICENSE file included (MIT)
- CHANGELOG.md with version history
- All commands working as documented
- Extension tested on a real project
- Command names follow speckit.{ext-id}.{command} pattern
- No old command references remaining
- Configuration template provided

## Next Steps

After this PR is merged:
1. The extension will be available in the main spec-kit repository at `spec-kit-github-issues/` 
2. Users can install it locally using `specify extension add --dev`
3. A follow-up PR can add this extension to the Community Extensions table in the main README   

**Note:** This extension is bundled with the main spec-kit repository. For a standalone
community extension, it would need to be moved to a separate repository with GitHub releases.
## Testing Screenshots

Successfully imported issue #2175 and generated spec:
- Created .specify/specs/001-generate-spec-artifacts-from-github-issues/spec.md
- Created .specify/specs/001-generate-spec-artifacts-from-github-issues/.issue-link
- Parsed 3 user stories with acceptance criteria
- Preserved discussion notes from comments