External integrations framework #7

Description

docsgraph-server should be able to connect to external systems (e.g. storage providers, identity providers, notification channels) without hardcoding each integration into the core.

Proposed Solution

Define an integrations framework (plugin/connector interface, configuration, auth handling) and implement one reference integration against it.

Acceptance Criteria

• Integration interface/framework is defined and documented
• At least one reference integration is implemented against the framework
• Integrations can be enabled/configured without core code changes
• Failing integrations degrade gracefully without affecting core sync/processing