Add Linear project triggers

[michaelmwu]

Summary

• Add Linear OAuth, signed webhooks, workspace connections, issue/comment triggers, and Linear replies.
• Support project, state, label, assignee, actor, comment, and assignment filtering, including project-scoped autonomous first-draft PR workflows.
• Add operator app setup, documentation, and a fresh current-main database migration.

Validation

• npm run typecheck
• npm run lint
• npm run format:check
• npm run db:check
• Focused Linear and provider-application Vitest suites, including PGlite OAuth bind safety.
• npm test reached container-backed integration tests, which cannot run here because no container runtime is available.