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/postgres/0001_create_networks.sql

@@ -0,0 +1,6 @@
+-- networks: IP address ranges managed by the IPAM.
+-- BIGSERIAL: auto-incrementing 64-bit integer (PostgreSQL's equivalent of AUTOINCREMENT).
+CREATE TABLE IF NOT EXISTS networks (
+    id   BIGSERIAL PRIMARY KEY,
+    cidr TEXT      NOT NULL UNIQUE
+);

migrations/postgres/0002_create_hosts.sql

@@ -0,0 +1,7 @@
+-- hosts: physical or virtual machines belonging to a network.
+CREATE TABLE IF NOT EXISTS hosts (
+    id         BIGSERIAL PRIMARY KEY,
+    name       TEXT   NOT NULL,
+    ip         TEXT   NOT NULL,
+    network_id BIGINT NOT NULL REFERENCES networks(id) ON DELETE CASCADE
+);

migrations/postgres/0003_create_ports.sql

@@ -0,0 +1,5 @@
+-- ports: global catalog of TCP/UDP port numbers and their known protocol.
+CREATE TABLE IF NOT EXISTS ports (
+    number      INTEGER PRIMARY KEY,
+    description TEXT
+);

migrations/postgres/0004_create_applications.sql

@@ -0,0 +1,5 @@
+-- applications: software stacks that use one or more ports.
+CREATE TABLE IF NOT EXISTS applications (
+    id   BIGSERIAL PRIMARY KEY,
+    name TEXT      NOT NULL
+);

migrations/postgres/0005_create_host_ports.sql

@@ -0,0 +1,6 @@
+-- host_ports: which ports are open on which host (many-to-many).
+CREATE TABLE IF NOT EXISTS host_ports (
+    host_id     BIGINT  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/postgres/0006_create_application_ports.sql

@@ -0,0 +1,6 @@
+-- application_ports: which ports an application typically uses (many-to-many).
+CREATE TABLE IF NOT EXISTS application_ports (
+    application_id BIGINT  NOT NULL REFERENCES applications(id) ON DELETE CASCADE,
+    port_number    INTEGER NOT NULL,
+    PRIMARY KEY (application_id, port_number)
+);