feat(seed): add dev seed binary with networks and hosts

Creates a self-contained `seed` binary (cargo run --features ssr --bin seed)
that loads realistic test data into the database. Idempotent: safe to run
multiple times without creating duplicates.

Data: 4 networks (LAN, DMZ, corporate, VPN) and 17 hosts spread across them.
Both SQLite and PostgreSQL seed files are provided.

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

seeds/postgres/dev_seed.sql

@@ -0,0 +1,63 @@
+-- dev_seed.sql (PostgreSQL) — development test data
+--
+-- Running this script is idempotent: existing rows are left untouched
+-- and missing rows are inserted.  Safe to run multiple times.
+--
+-- Load with: cargo run --features ssr --bin seed
+
+-- ── Networks ──────────────────────────────────────────────────────────────────
+
+INSERT INTO networks (cidr) VALUES
+    ('192.168.1.0/24'),
+    ('192.168.10.0/24'),
+    ('10.0.0.0/8'),
+    ('172.16.0.0/16')
+ON CONFLICT (cidr) DO NOTHING;
+
+-- ── Hosts ─────────────────────────────────────────────────────────────────────
+-- Hosts have no UNIQUE constraint, so we guard with WHERE NOT EXISTS.
+
+-- LAN — 192.168.1.0/24
+INSERT INTO hosts (name, ip, network_id)
+SELECT name, ip, (SELECT id FROM networks WHERE cidr = '192.168.1.0/24')
+FROM (VALUES
+    ('gateway',        '192.168.1.1'),
+    ('workstation-01', '192.168.1.10'),
+    ('workstation-02', '192.168.1.11'),
+    ('workstation-03', '192.168.1.12'),
+    ('nas-01',         '192.168.1.20'),
+    ('printer-01',     '192.168.1.50')
+) AS t(name, ip)
+WHERE NOT EXISTS (SELECT 1 FROM hosts WHERE hosts.name = t.name AND hosts.ip = t.ip);
+
+-- DMZ — 192.168.10.0/24
+INSERT INTO hosts (name, ip, network_id)
+SELECT name, ip, (SELECT id FROM networks WHERE cidr = '192.168.10.0/24')
+FROM (VALUES
+    ('web-server-01',  '192.168.10.10'),
+    ('web-server-02',  '192.168.10.11'),
+    ('db-server-01',   '192.168.10.20'),
+    ('mail-server-01', '192.168.10.30')
+) AS t(name, ip)
+WHERE NOT EXISTS (SELECT 1 FROM hosts WHERE hosts.name = t.name AND hosts.ip = t.ip);
+
+-- Corporate backbone — 10.0.0.0/8
+INSERT INTO hosts (name, ip, network_id)
+SELECT name, ip, (SELECT id FROM networks WHERE cidr = '10.0.0.0/8')
+FROM (VALUES
+    ('core-switch-01',   '10.0.0.1'),
+    ('monitoring-01',    '10.0.1.10'),
+    ('backup-server-01', '10.0.1.20'),
+    ('log-server-01',    '10.0.1.30')
+) AS t(name, ip)
+WHERE NOT EXISTS (SELECT 1 FROM hosts WHERE hosts.name = t.name AND hosts.ip = t.ip);
+
+-- VPN — 172.16.0.0/16
+INSERT INTO hosts (name, ip, network_id)
+SELECT name, ip, (SELECT id FROM networks WHERE cidr = '172.16.0.0/16')
+FROM (VALUES
+    ('vpn-gateway-01', '172.16.0.1'),
+    ('vpn-client-01',  '172.16.1.10'),
+    ('vpn-client-02',  '172.16.1.11')
+) AS t(name, ip)
+WHERE NOT EXISTS (SELECT 1 FROM hosts WHERE hosts.name = t.name AND hosts.ip = t.ip);