feat(db): add SQLx migrations and AppState with connection pool

- Add sqlx 0.8 (AnyPool, runtime-tokio, sqlite, postgres, migrate)
- Create 6 migration files for both SQLite and PostgreSQL backends
- Add server/db.rs: create_pool and run_migrations helpers
- Add server/state.rs: AppState with LeptosOptions + AnyPool
- Run migrations at server startup before accepting requests
- Fix Port model: remove host_id (ports are now a global catalog)
- Add HostPort join struct for the host_ports many-to-many table

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

migrations/sqlite/0001_create_networks.sql

@@ -0,0 +1,6 @@
+-- networks: IP address ranges managed by the IPAM.
+-- Each network has a unique CIDR block (e.g. "192.168.1.0/24").
+CREATE TABLE IF NOT EXISTS networks (
+    id   INTEGER PRIMARY KEY AUTOINCREMENT,
+    cidr TEXT    NOT NULL UNIQUE
+);

migrations/sqlite/0002_create_hosts.sql

@@ -0,0 +1,9 @@
+-- hosts: physical or virtual machines belonging to a network.
+-- The ip field must fall within the CIDR of the parent network
+-- (enforced in application code, not at the DB level).
+CREATE TABLE IF NOT EXISTS hosts (
+    id         INTEGER PRIMARY KEY AUTOINCREMENT,
+    name       TEXT    NOT NULL,
+    ip         TEXT    NOT NULL,
+    network_id INTEGER NOT NULL REFERENCES networks(id) ON DELETE CASCADE
+);

migrations/sqlite/0003_create_ports.sql

@@ -0,0 +1,7 @@
+-- ports: global catalog of TCP/UDP port numbers and their known protocol.
+-- Ports are not tied to a specific host here — host_ports handles that link.
+-- Port numbers range from 0 to 65535 (fits in INTEGER).
+CREATE TABLE IF NOT EXISTS ports (
+    number      INTEGER PRIMARY KEY,
+    description TEXT
+);

migrations/sqlite/0004_create_applications.sql

@@ -0,0 +1,6 @@
+-- applications: software stacks that use one or more ports.
+-- Examples: "Nginx", "PostgreSQL", "Prometheus".
+CREATE TABLE IF NOT EXISTS applications (
+    id   INTEGER PRIMARY KEY AUTOINCREMENT,
+    name TEXT    NOT NULL
+);

migrations/sqlite/0005_create_host_ports.sql

@@ -0,0 +1,7 @@
+-- host_ports: which ports are open on which host (many-to-many).
+-- Composite primary key prevents duplicate (host, port) pairs.
+CREATE TABLE IF NOT EXISTS host_ports (
+    host_id     INTEGER NOT NULL REFERENCES hosts(id) ON DELETE CASCADE,
+    port_number INTEGER NOT NULL REFERENCES ports(number) ON DELETE CASCADE,
+    PRIMARY KEY (host_id, port_number)
+);

migrations/sqlite/0006_create_application_ports.sql

@@ -0,0 +1,8 @@
+-- application_ports: which ports an application typically uses (many-to-many).
+-- port_number is not a strict FK to ports to allow registering an application
+-- before its port entry exists in the catalog.
+CREATE TABLE IF NOT EXISTS application_ports (
+    application_id INTEGER NOT NULL REFERENCES applications(id) ON DELETE CASCADE,
+    port_number    INTEGER NOT NULL,
+    PRIMARY KEY (application_id, port_number)
+);