Remove local modernize java plugin

[aaronpowell]

Removing plugin to replace with #1962

[github-actions]

🔒 PR Risk Scan Results

Scanned 3 changed file(s).

Severity	Count
🔴 High	0
🟠 Medium	0
ℹ️ Info	0

✅ No matching risk patterns were detected in changed files.

This is an automated soft-gate report. Findings indicate review targets and do not block merge by themselves.

[Copilot]

Pull request overview

Removes the locally-hosted modernize-java plugin and its associated agent/docs/listings from this repository, presumably in preparation for switching to the external plugin submission tracked in #1962.

Changes:

• Delete the local plugins/modernize-java plugin metadata and README.
• Remove the modernize-java agent markdown file and its entry from the agents index.
• Remove modernize-java from the plugins docs index and the generated marketplace catalog.

Show a summary per file

File	Description
plugins/modernize-java/README.md	Deletes the local plugin’s README content.
plugins/modernize-java/.github/plugin/plugin.json	Deletes the local plugin manifest used for marketplace generation.
docs/README.plugins.md	Removes the plugin entry from the plugins documentation index.
docs/README.agents.md	Removes the agent entry from the agents documentation index.
agents/modernize-java.agent.md	Deletes the local agent definition.
.github/plugin/marketplace.json	Removes modernize-java from the generated marketplace plugin list.

Copilot's findings

Comments suppressed due to low confidence (1)

.github/plugin/marketplace.json:588

• This PR removes the local modernize-java plugin from the generated marketplace list, but there’s no external replacement in plugins/external.json (no modernize-java entry found). That means users will lose the modernize-java install target until the external-plugin approval flow lands, which conflicts with the PR description (“replace with #1962”) and can introduce marketplace downtime.

To avoid a gap, please either (a) merge the automation-generated PR that adds modernize-java to plugins/external.json first (from issue #1962), then land this removal, or (b) include the external catalog entry + regenerated outputs in the same change (maintainer-only). At minimum, update this PR description to link the exact replacement PR and state the required merge order.

    {
      "name": "napkin",
      "source": "napkin",
      "description": "Visual whiteboard collaboration for Copilot CLI. Opens an interactive whiteboard in your browser where you can draw, sketch, and add sticky notes — then share everything back with Copilot. Copilot sees your drawings and responds with analysis, suggestions, and ideas.",
      "version": "1.0.0"

• Files reviewed: 6/6 changed files
• Comments generated: 0