feat(dhcp): DHCPv4-Server via Kea (kea-dhcp4-server) — v1.2.92

Verwalteter DHCPv4-Server analog Unbound/Squid/Chrony.
- Migration 0041: dhcp_settings (singleton, node-lokal), dhcp_subnets, dhcp_reservations.
- internal/kea: Renderer baut Kea-JSON via Go-Struct→Marshal (garantiert valide), managed /etc/edgeguard/kea/kea-dhcp4.conf (Symlink von /etc/kea), Service-Lifecycle an enabled gekoppelt (default AUS, kein rogue DHCP). Interface per NAME (cluster-sicher, kein node-lokaler FK).
- internal/services/dhcp + internal/handlers/dhcp.go: Settings + Subnet/Reservation-CRUD, Validierung (CIDR/IP/MAC/interface exists).
- configgen: Stop/Enable/DisableService. Firewall: AutoFWRule.Iface → udp/67 pro LAN-Interface gescopt (kein WAN). Cluster: subnets/reservations repliziert (hashSpec), dhcp_settings node-lokal (localOnlyTables).
- main.go + render.go + WithAllReloaders Wiring. Packaging: kea-dhcp4-server Dependency, /etc/edgeguard/kea Dir, Symlink, disable-on-install, sudoers (restart/stop/enable/disable).
- UI: DHCP-Seite (Settings + Subnets + Reservierungen pro Subnet), Route/Nav/i18n de/en, HA-Warnung 'nur auf einer Node aktivieren'.
- Tests (guarded EG_FWTEST_DSN): Kea-Renderer gegen DB (valides JSON + Felder), FW-Auto-Rule-Iface inkl. nft -c. Scope v1: DHCPv4.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

internal/database/migrations/0041_dhcp.sql

@@ -0,0 +1,62 @@
+-- +goose Up
+-- +goose StatementBegin
+
+-- DHCP (Kea) — globale Singleton-Settings (node-lokal, wie dns_settings/
+-- ntp_settings: ob DIESE Node DHCP betreibt). Subnets/Reservierungen sind
+-- geteilte Config und werden repliziert.
+CREATE TABLE IF NOT EXISTS dhcp_settings (
+    id             INTEGER     PRIMARY KEY DEFAULT 1,
+    enabled        BOOLEAN     NOT NULL DEFAULT false,
+    default_lease  INTEGER     NOT NULL DEFAULT 3600,
+    max_lease      INTEGER     NOT NULL DEFAULT 7200,
+    domain_name    TEXT        NOT NULL DEFAULT '',
+    dns_servers    TEXT        NOT NULL DEFAULT '',
+    created_at     TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    updated_at     TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    CONSTRAINT dhcp_settings_singleton CHECK (id = 1)
+);
+INSERT INTO dhcp_settings (id) VALUES (1) ON CONFLICT DO NOTHING;
+
+-- Subnets: an ein Interface per NAME gebunden (nicht per node-lokaler FK,
+-- damit die Replikation nicht an divergierenden interface_id bricht).
+CREATE TABLE IF NOT EXISTS dhcp_subnets (
+    id             BIGSERIAL   PRIMARY KEY,
+    name           TEXT        NOT NULL,
+    interface_name TEXT        NOT NULL,
+    subnet_cidr    TEXT        NOT NULL,
+    pool_start     TEXT        NOT NULL DEFAULT '',
+    pool_end       TEXT        NOT NULL DEFAULT '',
+    gateway        TEXT        NOT NULL DEFAULT '',
+    dns_servers    TEXT        NOT NULL DEFAULT '',
+    lease_time     INTEGER,
+    active         BOOLEAN     NOT NULL DEFAULT true,
+    description    TEXT        NOT NULL DEFAULT '',
+    created_at     TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    updated_at     TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    CONSTRAINT dhcp_subnets_name_unique UNIQUE (name)
+);
+
+CREATE TABLE IF NOT EXISTS dhcp_reservations (
+    id          BIGSERIAL   PRIMARY KEY,
+    subnet_id   BIGINT      NOT NULL REFERENCES dhcp_subnets(id) ON DELETE CASCADE,
+    name        TEXT        NOT NULL DEFAULT '',
+    mac_address TEXT        NOT NULL,
+    ip_address  TEXT        NOT NULL,
+    hostname    TEXT        NOT NULL DEFAULT '',
+    active      BOOLEAN     NOT NULL DEFAULT true,
+    created_at  TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    updated_at  TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    CONSTRAINT dhcp_reservations_subnet_mac_unique UNIQUE (subnet_id, mac_address)
+);
+CREATE INDEX IF NOT EXISTS idx_dhcp_reservations_subnet ON dhcp_reservations(subnet_id);
+
+-- +goose StatementEnd
+
+-- +goose Down
+-- +goose StatementBegin
+
+DROP TABLE IF EXISTS dhcp_reservations;
+DROP TABLE IF EXISTS dhcp_subnets;
+DROP TABLE IF EXISTS dhcp_settings;
+
+-- +goose StatementEnd