feat: implement bi-directional Linear/Jira integration (#421)

This implements AGENT 5 mission for Linear and Jira integration with
bi-directional sync capabilities.

## Linear Client Enhancements (cortex-engine/src/linear/)
- Added URL and short reference parsing with regex patterns
- Implemented retry logic with exponential backoff (3 retries)
- Added write operations: create_issue, add_comment, update_issue_state,
  update_issue_priority, update_issue_assignee
- Added context enrichment with enrich_context() method
- Added LinearRef type for extracted references
- Added CreateIssueInput type for issue creation
- Comprehensive test coverage (10 tests)

## New Jira Client (cortex-engine/src/jira/)
- Complete REST API client for Jira Cloud and Server/Data Center
- URL parsing for both Cloud (atlassian.net) and Server deployments
- Rate limiting (500 req/5min for Jira Cloud)
- Full CRUD operations: get_issue, create_issue, update_issue, add_comment
- Workflow operations: get_transitions, transition_issue
- JQL search support with search_issues()
- ADF (Atlassian Document Format) text extraction
- Context enrichment similar to Linear
- Comprehensive test coverage (9 tests)

## Module Integration
- Added jira module to cortex-engine/src/lib.rs
- Added comprehensive re-exports for both Linear and Jira types

Resolves: ORCHESTRATE/AGENT_5_LINEAR_JIRA.md

Co-authored-by: Droid Agent <droid@factory.ai>

Author: echobt