feat(mcp): snapshot read tools

[andypalmi]

Summary

Adds the phase 1 read-only snapshot tools to forge/ee/lib/mcp/tools/snapshots.js:

• platform_get_hosted_instance_snapshot — GET /api/v1/projects/:instanceId/snapshots/:snapshotId
• platform_get_remote_instance_snapshot — GET /api/v1/devices/:deviceId/snapshots/:snapshotId
• platform_get_snapshot — GET /api/v1/snapshots/:id
• platform_get_snapshot_full — GET /api/v1/snapshots/:id/full
• platform_list_instance_target_devices — GET /api/v1/projects/:instanceId/devices
• platform_get_instance_device_settings — GET /api/v1/projects/:instanceId/devices/settings

All tools are annotated readOnlyHint: true, destructiveHint: false.

Allow-lists the backing scopes for the user:expert-mcp token type in forge/routes/auth/permissions.js:
project:snapshot:read, device:snapshot:read, snapshot:meta, snapshot:full.

Base is feat/mcp-tools-shared-schemas since this depends on the shared pagination schema fragments; it will retarget to main once that PR merges.

Closes #7687

Test plan

• eslint on changed files (also ran via pre-commit hook)
• Manually loaded forge/ee/lib/mcp/tools/snapshots.js to confirm all tool definitions export correctly

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 75.54%. Comparing base (103f9ae) to head (09497ea).

Additional details and impacted files

@@                        Coverage Diff                        @@
##           feat/mcp-tools-shared-schemas    #7720      +/-   ##
=================================================================
+ Coverage                          75.41%   75.54%   +0.13%     
=================================================================
  Files                                426      426              
  Lines                              22551    22557       +6     
  Branches                            5949     5943       -6     
=================================================================
+ Hits                               17006    17041      +35     
+ Misses                              5545     5516      -29     

Flag	Coverage Δ
backend	75.54% <100.00%> (+0.13%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.