feat(networks): add name field to networks

- Migration 0007: ALTER TABLE networks ADD COLUMN name TEXT NOT NULL DEFAULT ''
- Network model, repository, and API updated to include name
- Networks page: name input in the add form, Name column as first column in table
- Delete modal now shows "Name (CIDR)" for clarity
- Hosts page: network dropdowns now show network name instead of CIDR
- Seeds updated with names (LAN, DMZ, Corporate, VPN)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/models.rs

@@ -28,6 +28,9 @@ pub struct Network {
     /// `i64` is a signed 64-bit integer — maps to `BIGINT` in SQL.
     pub id: i64,
 
+    /// Human-readable name. Examples: "LAN", "DMZ", "VPN"
+    pub name: String,
+
     /// Address range in CIDR notation.
     /// Examples: "10.0.0.0/8", "172.16.0.0/12", "192.168.1.0/24"
     pub cidr: String,