[connectors] feat: add Linear connector for web-security

[GangGreenTemperTatum]

Summary

Adds a Linear MCP connector to the web-security capability so validated findings can be exported as Linear remediation issues.

The connector is designed as a portable capability-local GraphQL integration instead of relying on ambient Linear tooling. It keeps issue creation in the post-validation delivery path and updates the web-security agent guidance accordingly.

Changes

• Adds capabilities/web-security/mcp/linear.py as a self-contained uv run FastMCP server.
• Wires the linear MCP server into capabilities/web-security/capability.yaml.
• Adds agent prompt guidance for Linear export behavior and required credentials.
• Adds focused tests for API key/OAuth auth handling, GraphQL error handling, team listing, issue creation, issue fetch, and comment creation.

Connector Surface

• linear_health
• linear_list_teams
• linear_create_issue
• linear_get_issue
• linear_add_comment

Auth supports LINEAR_API_KEY or LINEAR_ACCESS_TOKEN, with optional LINEAR_API_URL override.

Validation

• uv run pytest capabilities/web-security/tests/test_linear_mcp.py passed: 11 tests.
• mypy capabilities/web-security/mcp/linear.py capabilities/web-security/tests/test_linear_mcp.py --ignore-missing-imports passed.
• pre-commit run --files capabilities/web-security/capability.yaml capabilities/web-security/agents/web-security.md capabilities/web-security/mcp/linear.py capabilities/web-security/tests/test_linear_mcp.py passed.
• just validate completed with 0 failures.
• MCP startup smoke passed via uv run capabilities/web-security/mcp/linear.py; process stayed running until timeout as expected for stdio MCP.
• PYTHONPATH=capabilities/web-security/tools uv run pytest capabilities/web-security/tests passed: 147 passed, 7 existing warnings.
• git diff --check passed.

Known just validate warnings are pre-existing environment warnings unrelated to this change: bloodhound-enterprise runtime imports, local web-security caido-cli/Burp checks, and windows-reversing Java 17 check.