fix(plugins): merge git collection into rpi and distribute to all plugins

Description

Consolidated the standalone git collection into the rpi collection, removing plugins/git/ entirely and distributing git-related agents, prompts, and instructions across all remaining plugin bundles. Since RPI is the foundational collection included by every other collection, git workflow tooling now ships as part of the baseline rather than as a separate opt-in package.

• Deleted collections/git.collection.yml and collections/git.collection.md, merging all git items (pr-review agent, five git prompts, git-merge instruction) into collections/rpi.collection.yml
• Removed plugins/git/ directory including its plugin.json, README.md, all agent/command/instruction symlinks, and script directory links
• Added pr-review agent, git prompts (git-commit-message, git-commit, git-merge, git-setup, pull-request), and git-merge instruction to all nine remaining collection YMLs (ado, coding-standards, data-science, github, project-planning, prompt-engineering, rpi, security-planning, hve-core-all)
• Created corresponding symlinks and updated README tables for each plugin bundle to surface the newly included git commands, pr-review agent, and git-merge instruction
• Updated rpi plugin description to reflect the merged scope
• Removed the git entry from .github/plugin/marketplace.json

Related Issue(s)

Type of Change

Select all that apply:

Code & Documentation:

• Bug fix (non-breaking change fixing an issue)
• New feature (non-breaking change adding functionality)
• Breaking change (fix or feature causing existing functionality to change)
• Documentation update

Infrastructure & Configuration:

• GitHub Actions workflow
• Linting configuration (markdown, PowerShell, etc.)
• Security configuration
• DevContainer configuration
• Dependency update

AI Artifacts:

• Reviewed contribution with prompt-builder agent and addressed all feedback
• Copilot instructions (.github/instructions/*.instructions.md)
• Copilot prompt (.github/prompts/*.prompt.md)
• Copilot agent (.github/agents/*.agent.md)
• Copilot skill (.github/skills/*/SKILL.md)

Note for AI Artifact Contributors:

• Agents: Research, indexing/referencing other project (using standard VS Code GitHub Copilot/MCP tools), planning, and general implementation agents likely already exist. Review .github/agents/ before creating new ones.
• Skills: Must include both bash and PowerShell scripts. See Skills.
• Model Versions: Only contributions targeting the latest Anthropic and OpenAI models will be accepted. Older model versions (e.g., GPT-3.5, Claude 3) will be rejected.
• See Agents Not Accepted and Model Version Requirements.

Other:

• Script/automation (.ps1, .sh, .py)
• Other (please describe):

Sample Prompts (for AI Artifact Contributions)

Testing

Checklist

Required Checks

• Documentation is updated (if applicable)
• Files follow existing naming conventions
• Changes are backwards compatible (if applicable)
• Tests added for new functionality (if applicable)

AI Artifact Contributions

Required Automated Checks

The following validation commands must pass before merging:

• Markdown linting: npm run lint:md
• Spell checking: npm run spell-check
• Frontmatter validation: npm run lint:frontmatter
• Link validation: npm run lint:md-links
• PowerShell analysis: npm run lint:ps

Security Considerations

• This PR does not contain any sensitive or NDA information
• Any new dependencies have been reviewed for security issues
• Security-related scripts follow the principle of least privilege

Additional Notes

• Version files (package.json, package-lock.json, .release-please-manifest.json, extension/templates/package.template.json, all plugin.json files, and marketplace.json) regressed from 2.3.5 to 2.3.4, and the CHANGELOG.md entry for 2.3.5 was removed. Confirm this version rollback is intentional or rebase onto the current origin/main to pick up the 2.3.5 release.

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