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>

seeds/sqlite/dev_seed.sql

@@ -6,12 +6,11 @@
 -- Load with: cargo run --features ssr --bin seed
 
 -- ── Networks ──────────────────────────────────────────────────────────────────
--- INSERT OR IGNORE relies on the UNIQUE constraint on cidr.
 
-INSERT OR IGNORE INTO networks (cidr) VALUES ('192.168.1.0/24');
-INSERT OR IGNORE INTO networks (cidr) VALUES ('192.168.10.0/24');
-INSERT OR IGNORE INTO networks (cidr) VALUES ('10.0.0.0/8');
-INSERT OR IGNORE INTO networks (cidr) VALUES ('172.16.0.0/16');
+INSERT OR IGNORE INTO networks (name, cidr) VALUES ('LAN',       '192.168.1.0/24');
+INSERT OR IGNORE INTO networks (name, cidr) VALUES ('DMZ',       '192.168.10.0/24');
+INSERT OR IGNORE INTO networks (name, cidr) VALUES ('Corporate', '10.0.0.0/8');
+INSERT OR IGNORE INTO networks (name, cidr) VALUES ('VPN',       '172.16.0.0/16');
 
 -- ── Hosts ─────────────────────────────────────────────────────────────────────
 -- Hosts have no UNIQUE constraint, so we guard each insert with WHERE NOT EXISTS.