Add continuous maintenance scan workflow (#1)

[last-light]

Closes #1

Summary

• Adds a weekly continuous maintenance scan cron workflow for repository health checks.
• Introduces a maintenance-review workflow and skill contract for dashboard issue creation, delta scans, dedupe, caps, and cleanup.
• Grants the maintenance review workflow issues-write permissions so it can manage GitHub issues.
• Adds workflow loader and permission mapping tests for the new maintenance review path.

Planning and execution docs

• Guardrails report
• Architect plan
• Executor summary
• Reviewer verdict
• Status

Test results

Command: npm test

> lastlight@0.1.15 test
> vitest run


 RUN  v4.1.7 /home/agent/workspace/lastlight


 Test Files  22 passed (22)
      Tests  401 passed | 1 todo (402)
   Start at  15:01:52
   Duration  4.99s (transform 524ms, setup 0ms, import 1.00s, tests 1.95s, environment 1ms)

No lint command is configured in package.json; guardrails report marks linting as missing / not run.

Command: npm run build

> lastlight@0.1.15 build
> tsc