feat: add Copilot Agent Plugins and MCP inventory

[raysubham]

What does this PR do?

Adds Copilot CLI, standalone Copilot app and VS Code Agent Plugins inventory to the existing plugin scan phase. Collects recorded installations and persistent local-marketplace selections, their supplied skills, custom-agent declarations and sanitized MCP definitions, plus standalone user/project MCP configurations. Preserves source, scope, enablement observations and parent relationships without treating cached directories as installed plugins.

Reuses bounded, file-only readers and TCC protection. Git/GitHub catalogs support complete component coverage when matching evidence is readable; failed reads remain partial. Regression tests preserve shared MCP symlinks and unrelated project MCP configurations. Copilot cases are consolidated into the common Agent Plugins golden fixture with Claude/Codex. Matching API fixture/test updates are in main PR #11029 and integration follow-up #11093. Existing AITool inventory and internal/aiagents are unchanged.

Copilot tests use the existing shared plugin, MCP and model test files. Production adapters retain the existing per-agent file pattern.

Type of change

• Enhancement
• Documentation

Testing

• Full go test -race ./..., plus affected-package regression tests
• go vet ./..., golangci-lint run ./..., formatting and whitespace checks
• go mod tidy -diff with no dependency drift
• make smoke: 45/45 checks passed
• CGO-disabled builds for Linux amd64, macOS arm64 and Windows amd64
• Shared fixture: DMG contract test and existing API fixture/lifecycle tests passed
• Pinned Copilot 1.0.91 native-format probes in an isolated offline environment
• No secrets or credentials included

Gosec completed with no package-load errors and the same 24 pre-existing findings. The four original local review findings were fixed and revalidated. Expanded native-surface limitations are tracked in the live runbook.

Native CLI core lifecycle was checked on macOS, Linux and Windows. Expanded Mac checks cover five app marketplace plugins, three editor/Agents marketplace selections, project local-source registration, toggles/removal and integration Skills/MCP supplier links. Commands, rules and LSP declarations were added with regression tests and a native packaged-fixture check. Rules carry declaration metadata only; CLI runtime activation is not claimed. Expanded Windows/Linux app/editor checks and app-only local GUI lifecycle remain pending. Deployed rule-kind acceptance passed on Mac. Editor activation stays unknown where its private state is not collected. TCC-protected paths remain guarded.

Follow-up commit: 8b8e85c, signature verified. Shared fixture SHA-256: 4aa872e1df3d2c33326cd43193d17f7c0b1d36ce0a4e4f3734af8e0b3144215b. Backend rule-kind acceptance from #11093 is deployed and verified on integration. Release the matching backend changes before this candidate in production.

Custom-catalog follow-up: signed commit dcdb8fb resolves editor file-URI catalogs to their validated Git payload provenance. Native VS Code installation from the owned private catalog, stable identity across CLI/editor, four linked skill/command rows, unselected-entry exclusion and post-uninstall API restoration passed. Missing/mismatched/protected catalogs have regression coverage. Full local gates passed. Latest DMG CI passed Test; remaining jobs were cancelled before execution because hosted runners were not acquired. DMG/main release PRs remain unmerged; API integration follow-up #11093 is merged and deployed.

Post-deployment Mac retest: exact skill/command/rule/LSP details, all four kind filters and skill/command supplier refs passed. Native CLI uninstall and restored API checks passed: six plugin groups, nine installations, 23 linked skills and exact MCP supplier refs. Claude/Codex control IDs and skill hashes match the earlier baseline. No new product fix was needed. Latest DMG CI passed tests, but other jobs could not acquire hosted runners; full CI is not green.

Standalone Mac app custom local-catalog selection passed: the user enabled incident-review through the app. DMG and deployed APIs agree on its single local installation, complete skill component, identity and content hash. Native uninstall for this live plugin only disables it; the backend correctly retained the same installation/skill with configured_enabled=false. This is not a GUI uninstall pass. The app's private Git clone failed authentication despite working shell Git/GitHub access; that native-app/setup limitation remains logged, not reported as a collector defect. Existing Claude/Codex control records remain unchanged.

[raysubham]

Live integration validation found an editor marketplace identity mismatch. Signed commit cbe8792 preserves the receipt marketplace reference instead of overwriting it with the catalog display name; a regression assertion covers the ID/name contract. Synced current main in signed ba5df7e so the full existing workflow uses a compatible candidate, including already-merged Go inventory. Full race tests, lint, vet, 45 smoke checks and three-platform builds passed. Full three-platform Developer MDM V1 run: https://github.com/step-security/integration-test/actions/runs/37526699915. Live acceptance remains in progress; this PR is not merged.