Add Support for Linear

[dawilco]

Add a Linear harness that is functionally similar to JIRA

[dawilco]

Implemented in #27 — full Linear integration with autonomous backlog processing:

Baseline:

• Linear as automation source (polls issues via GraphQL API)
• Output handlers: comment, transition, create issue
• Settings > Linear page with API key config and test connection
• 87 tests

Beyond JIRA parity — autonomous backlog processing:

• update_linear_issue, create_linear_issue, get_linear_issue MCP tools
• Linear-to-Kanban bridge (auto-creates kanban tasks from polled issues)
• Queue system with sequential/concurrent/parallel modes and auto-advance
• Bidirectional status sync (kanban ↔ Linear)
• Git workflow automation (branch naming, PR instructions per ticket)
• Backlog progress UI with real-time stats