feat: add Calendly service configuration

[shreyanshjain7174]

Closes #12.

What changed:

• Adds Calendly as a bearer-token service at https://api.calendly.com.
• Adds the read-only GET /scheduled_events action with required user and optional count parameters.
• Keeps Docker, local development, and standalone service config aligned.
• Adds production-config tests that load all 3 configuration sources.

Verification:

• go test ./internal/registry -run TestProductionConfig_CalendlyListsScheduledEvents -count=1 -v
• go test ./internal/registry -run TestProductionConfig_LocalDevDefaultMatches -count=1 -v
• go test ./... -race -count=1
• go vet ./...
• git diff --check

All passed locally.

[Copilot]

Pull request overview

This PR adds Calendly to AgentGate’s service registry so agents can call the Calendly API through the existing config-driven gateway flow.

Changes:

• Add a new calendly bearer-token service pointing at https://api.calendly.com.
• Register the read-only list_scheduled_events action as GET /scheduled_events with user (required) and count (optional) params.
• Add a production-config test that validates Calendly is present and consistent across the 3 config sources.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
internal/registry/production_config_test.go	Adds a test that loads each config source and asserts Calendly service and action shape. Updates the local-dev drift guard to include Calendly.
configs/services/calendly.yaml	Adds the per-service reference YAML for Calendly.
configs/services.yaml	Adds Calendly to the Docker and quickstart-loaded registry config.
config/services.yaml	Adds Calendly to the local non-Docker dev default config.

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