rework: migrate module path, fix healthcheck URL, add architecture notes

- Migrate Go module path from git.eeqj.de/sneak/webhooker to
  sneak.berlin/go/webhooker (go.mod, pkg/config/go.mod, all imports)
- Drop .json extension from healthcheck endpoint: /.well-known/healthcheck
  (routes.go, Dockerfile HEALTHCHECK, README)
- Add Rate Limiting section to README Design: global rate limiting must
  not apply to webhook endpoints; per-webhook configurable limits instead
- Add Database Architecture section to README Design: separate SQLite
  files for main app config vs per-processor data (input logs, processor
  logs, output queues)

Addresses review feedback from sneak on PR #6.

internal/middleware/middleware.go

@@ -6,9 +6,6 @@ import (
 	"net/http"
 	"time"
 
-	"git.eeqj.de/sneak/webhooker/internal/config"
-	"git.eeqj.de/sneak/webhooker/internal/globals"
-	"git.eeqj.de/sneak/webhooker/internal/logger"
 	basicauth "github.com/99designs/basicauth-go"
 	"github.com/go-chi/chi/middleware"
 	"github.com/go-chi/cors"
@@ -16,6 +13,9 @@ import (
 	ghmm "github.com/slok/go-http-metrics/middleware"
 	"github.com/slok/go-http-metrics/middleware/std"
 	"go.uber.org/fx"
+	"sneak.berlin/go/webhooker/internal/config"
+	"sneak.berlin/go/webhooker/internal/globals"
+	"sneak.berlin/go/webhooker/internal/logger"
 )
 
 // nolint:revive // MiddlewareParams is a standard fx naming convention