Add comprehensive daemon mode support to pkg/cli:
- Mode detection (Interactive/Pipe/Daemon) based on TTY and CORE_DAEMON env
- TTY helpers using golang.org/x/term (IsTTY, IsStdinTTY, IsStderrTTY)
- PIDFile for single-instance enforcement with stale PID detection
- HealthServer with /health and /ready endpoints for orchestration
- Daemon lifecycle manager combining PID, health, and graceful shutdown
- SIGHUP support for configuration reloading in runtime.go
- Fix i18n.go type references (MissingKey, OnMissingKey)
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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