feat(mcp): add tool categorization/grouping to `loopover-mcp tools` output

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Context

Part of #6226. With ~150 tools combined across both MCP servers and no categorization today, loopover-mcp tools's flat list is hard to scan. Grouping by rough category (git/branch analysis, review/gate prediction, agent planning, maintainer/repo-owner actions, cache/config) would make the tool surface navigable, and pairs naturally with the sibling tool-search feature filed alongside this issue.

Requirements

• Add a category field to each tool's registration metadata (both packages/loopover-mcp/bin/loopover-mcp.js and src/mcp/server.ts, so the categorization is consistent across both servers — check with Spec: should local (@loopover/mcp) and remote (src/mcp/server.ts) MCP tool implementations share a core? #6227's shared-core work to avoid duplicating this metadata if that spec's outcome provides a shared registration point).
• Update loopover-mcp tools/tools --json to group output by category (human-readable output shows category headers; --json output includes the category field per tool).
• Choose category names based on this repo's own existing conceptual groupings (AMS-side vs. ORB-side vs. maintainer-facing vs. utility/config) rather than inventing an arbitrary taxonomy.

Test Coverage Requirements

Match this package's existing test conventions; a test confirming every registered tool has exactly one category and the grouped output reflects it.

Deliverables

• Every tool has a category.
• tools/tools --json output is grouped/annotated by category.

Expected Outcome

A user scanning the full tool list can quickly find the relevant subset instead of reading ~150 flat entries.

Links & Resources

• Epic: MCP platform — shared-core decision + usage telemetry #6226 (parent epic)
• The sibling tools search feature issue (natural pairing)

[linear-code]

JSO-4399