feat: implement GET /api/v1/domains and /api/v1/hostnames endpoints

Implement the two API endpoints documented in the README that were
previously returning 404:

- GET /api/v1/domains: Returns configured domains with their
  discovered nameservers, last check time, and status (ok/pending).

- GET /api/v1/hostnames: Returns configured hostnames with
  per-nameserver DNS records, status, and last check time.

Both endpoints read from the existing state store and config,
requiring no new dependencies. Nameserver results in the hostnames
endpoint are sorted for deterministic output.

Closes #67

internal/handlers/handlers.go

@@ -8,9 +8,11 @@ import (
 
 	"go.uber.org/fx"
 
+	"sneak.berlin/go/dnswatcher/internal/config"
 	"sneak.berlin/go/dnswatcher/internal/globals"
 	"sneak.berlin/go/dnswatcher/internal/healthcheck"
 	"sneak.berlin/go/dnswatcher/internal/logger"
+	"sneak.berlin/go/dnswatcher/internal/state"
 )
 
 // Params contains dependencies for Handlers.
@@ -20,6 +22,8 @@ type Params struct {
 	Logger      *logger.Logger
 	Globals     *globals.Globals
 	Healthcheck *healthcheck.Healthcheck
+	State       *state.State
+	Config      *config.Config
 }
 
 // Handlers provides HTTP request handlers.
@@ -28,6 +32,8 @@ type Handlers struct {
 	params  *Params
 	globals *globals.Globals
 	hc      *healthcheck.Healthcheck
+	state   *state.State
+	config  *config.Config
 }
 
 // New creates a new Handlers instance.
@@ -37,6 +43,8 @@ func New(_ fx.Lifecycle, params Params) (*Handlers, error) {
 		params:  &params,
 		globals: params.Globals,
 		hc:      params.Healthcheck,
+		state:   params.State,
+		config:  params.Config,
 	}, nil
 }
 
@@ -44,7 +52,7 @@ func (h *Handlers) respondJSON(
 	writer http.ResponseWriter,
 	_ *http.Request,
 	data any,
-	status int,
+	status int, //nolint:unparam // general-purpose utility; status varies in future use
 ) {
 	writer.Header().Set("Content-Type", "application/json")
 	writer.WriteHeader(status)