projects: update fields and prompt

[tmelliottjr]

Towards: https://github.com/github/memex/issues/20735

This pull request makes significant changes to how GitHub Project items are represented and handled in the codebase. The main updates involve removing the custom MinimalProjectItem type in favor of using the "full" projectV2Item structure which contained the same attributes, updating the project item schema to include richer content details, and improving the user prompt for managing GitHub Projects V2 with more comprehensive guidance and workflow examples.

The changes to the structs was necessary to ensure we have enough information to support complete workflows with projects, such as identifying the repository owner/name for additional requests.

[Copilot]

Pull Request Overview

This pull request modernizes the GitHub Projects V2 integration by replacing the custom MinimalProjectItem type with the richer projectV2Item structure and significantly enhancing the project management prompt with comprehensive workflows and guidance.

Key changes:

• Removed the MinimalProjectItem type and its conversion function, using the full projectV2Item structure instead to provide more detailed content information
• Added projectV2ItemContent struct with repository, issue/PR details, and state information to enable complete workflows
• Expanded the ManageProjectItems prompt with detailed workflows, examples, and guidance for cross-tool integration

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 16 comments.

File	Description
pkg/github/projects.go	Updated tool descriptions to use consistent JSON example format; removed conversions to MinimalProjectItem; expanded projectV2Item struct with new fields including nested content; enhanced ManageProjectItems prompt with comprehensive workflows and multi-tool guidance
pkg/github/minimal_types.go	Removed MinimalProjectItem type definition and convertToMinimalProjectItem helper function

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