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-server/internal/models/agent.go

@@ -63,12 +63,13 @@ type AgentSpecs struct {
 
 // AgentRegistrationRequest is the payload for agent registration
 type AgentRegistrationRequest struct {
-	Hostname       string            `json:"hostname" binding:"required"`
-	OSType         string            `json:"os_type" binding:"required"`
-	OSVersion      string            `json:"os_version"`
-	OSArchitecture string            `json:"os_architecture"`
-	AgentVersion   string            `json:"agent_version" binding:"required"`
-	Metadata       map[string]string `json:"metadata"`
+	Hostname         string            `json:"hostname" binding:"required"`
+	OSType           string            `json:"os_type" binding:"required"`
+	OSVersion        string            `json:"os_version"`
+	OSArchitecture   string            `json:"os_architecture"`
+	AgentVersion     string            `json:"agent_version" binding:"required"`
+	RegistrationToken string           `json:"registration_token"` // Optional, for fallback method
+	Metadata         map[string]string `json:"metadata"`
 }
 
 // AgentRegistrationResponse is returned after successful registration