Add systemd service/timer units for autonomous agent operation

Summary

• Per-agent systemd service units generated from roster config
• Automatic mode selection: continuous for maintainer-level (C-suite), timer for developer/reporter agents
• serviceMode option (continuous | timer | disabled) with override per agent
• timerInterval option for systemd calendar expression
• resources submodule (memoryMax, cpuQuota) for per-agent resource limits
• reporting submodule for GitLab issue creation (Option A from #9 (closed) discussion)
• secretsDirectory option with EnvironmentFile placeholder for #7
• claudeCommand option for Claude CLI invocation

Closes #9 (closed)

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