Implement per-service disk usage monitoring

Replaced system-wide disk usage with accurate per-service tracking by scanning
service-specific directories. Services like sshd now correctly show minimal
disk usage instead of misleading system totals.

- Rename storage widget and add drive capacity/usage columns
- Move host display to main dashboard title for cleaner layout
- Replace separate alert displays with color-coded row highlighting
- Add per-service disk usage collection using du command
- Update services widget formatting to handle small disk values
- Restructure into workspace with dedicated agent and dashboard packages

agent/src/collectors/mod.rs

@@ -0,0 +1,49 @@
+use async_trait::async_trait;
+use chrono::{DateTime, Utc};
+use serde_json::Value;
+use std::time::Duration;
+
+pub mod backup;
+pub mod error;
+pub mod service;
+pub mod smart;
+
+pub use error::CollectorError;
+
+#[derive(Debug, Clone)]
+pub enum AgentType {
+    Smart,
+    Service,
+    Backup,
+}
+
+impl AgentType {
+    pub fn as_str(&self) -> &'static str {
+        match self {
+            AgentType::Smart => "smart",
+            AgentType::Service => "service",
+            AgentType::Backup => "backup",
+        }
+    }
+}
+
+#[derive(Debug, Clone)]
+pub struct CollectorOutput {
+    pub agent_type: AgentType,
+    pub data: Value,
+    pub timestamp: DateTime<Utc>,
+}
+
+#[async_trait]
+pub trait Collector: Send + Sync {
+    fn name(&self) -> &str;
+    fn agent_type(&self) -> AgentType;
+    fn collect_interval(&self) -> Duration;
+    async fn collect(&self) -> Result<CollectorOutput, CollectorError>;
+    fn is_enabled(&self) -> bool {
+        true
+    }
+    fn requires_root(&self) -> bool {
+        false
+    }
+}