Release v0.3 — Reliability, self-update, and test coverage

[mateusmetzker]

Description

Merges dev into master for the v0.3 release.

PRs included

• Reliability improvements, self-update, and test coverage #4

Highlights

• Self-update via dashboard — binary update from the UI with SSE progress and automatic restart
• TunnelMonitor — automatic SSH tunnel reconnection with real-time SSE status
• 155 unit tests — coverage from zero across cli, config, docker, handler, metrics, and updater packages
• CI workflow — tests run automatically on push/PR to master and dev
• HTTP hardening — body size limits, method enforcement, JSON validation, WebSocket origin check
• Label-based container detection with network fallback
• Local metrics migrated to gopsutil v4

Breaking changes

• Install path changed from /usr/local/bin to ~/.local/bin to allow self-update without sudo
• model.Metrics struct changed due to gopsutil v4 migration — consumers of the metrics API may be affected