Add developer dashboard metrics endpoints

[roncodes]

Summary

• Add DeveloperMetricsController under the internal v1 namespace.
• Add internal developer dashboard aggregate metrics endpoints under int/v1/metrics/dev/*.
• Provide company-scoped KPI, API traffic, webhook delivery, credential, event, endpoint health, and recent activity aggregates for the developer console dashboard.
• Add Webhook Failures and Events Emitted KPI metrics for the balanced dashboard KPI set.
• Use the codebase-standard request input path for period parsing so the metrics endpoints do not 400 on older request contracts.
• Return aggregate metadata only and avoid exposing API key secrets, request bodies, response bodies, or webhook payload bodies.

Companion PR

This powers the redesigned developer console dashboard in the companion dev-engine PR:

• Refactor developer dashboard widgets dev-engine#40

Validation

• php -l src/Http/Controllers/Internal/v1/DeveloperDashboardController.php
• php -l src/routes.php
• composer test:lint was attempted, but Composer exits with code -1 and no output in this scratch worktree; composer --version has the same behavior and vendor/bin/php-cs-fixer is not present.

Documentation and API Reference Impact

• These endpoints are internal console metrics endpoints, not public Fleetbase API endpoints.
• No fleetbase/postman API spec update is expected.
• No fleetbase/fleetbase.io documentation update is expected for this backend-only internal metrics support.

[roncodes]

Superseded by the combined metrics API PR: #221