feat(mcp): device group read tools

[andypalmi]

Summary

Add Phase 1 read-only MCP tools for fleet device groups, per Story 5 sub-issue 5.6-a.

Tools added (forge/ee/lib/mcp/tools/deviceGroups.js):

• platform_list_application_device_groups — GET /api/v1/applications/:applicationId/device-groups
• platform_get_application_device_group — GET /api/v1/applications/:applicationId/device-groups/:groupId
• platform_list_team_device_groups — GET /api/v1/teams/:teamId/device-groups

All three routes require the deviceGroups team feature; when disabled they return the platform's existing 404 gate response.

Scopes allow-listed for user:expert-mcp in forge/routes/auth/permissions.js:

• application:device-group:list
• application:device-group:read
• team:device-group:list

Write, membership, settings, and delete tools are tracked separately in sub-issues 5.6-b/c and are not part of this PR.

Closes #7699

Test plan

• eslint on changed files
• Manual review of route mounts against forge/ee/routes/index.js, applicationDeviceGroups/index.js, teamDeviceGroups/index.js

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 75.42%. Comparing base (103f9ae) to head (f462226).

Additional details and impacted files

@@                        Coverage Diff                        @@
##           feat/mcp-tools-shared-schemas    #7719      +/-   ##
=================================================================
+ Coverage                          75.41%   75.42%   +0.01%     
=================================================================
  Files                                426      427       +1     
  Lines                              22551    22565      +14     
  Branches                            5949     5949              
=================================================================
+ Hits                               17006    17020      +14     
  Misses                              5545     5545              

Flag	Coverage Δ
backend	75.42% <100.00%> (+0.01%)	⬆️

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