v0.1.17: UI fixes, Linux improvements, documentation overhaul

UI/UX:
- Fix heartbeat auto-refresh and rate-limiting page
- Add navigation breadcrumbs to settings pages
- New screenshots added

Linux Agent v0.1.17:
- Fix disk detection for multiple mount points
- Improve installer idempotency
- Prevent duplicate registrations

Documentation:
- README rewrite: 538→229 lines, homelab-focused
- Split docs: API.md, CONFIGURATION.md, DEVELOPMENT.md
- Add NOTICE for Apache 2.0 attribution

aggregator-agent/internal/config/config.go

@@ -349,6 +349,12 @@ func (c *Config) Save(configPath string) error {
 		return fmt.Errorf("failed to marshal config: %w", err)
 	}
 
+	// Create parent directory if it doesn't exist
+	dir := filepath.Dir(configPath)
+	if err := os.MkdirAll(dir, 0755); err != nil {
+		return fmt.Errorf("failed to create config directory: %w", err)
+	}
+
 	if err := os.WriteFile(configPath, data, 0600); err != nil {
 		return fmt.Errorf("failed to write config: %w", err)
 	}