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/config/config.go

@@ -5,10 +5,10 @@ import (
 	"log/slog"
 	"os"
 
-	"git.eeqj.de/sneak/webhooker/internal/globals"
-	"git.eeqj.de/sneak/webhooker/internal/logger"
-	pkgconfig "git.eeqj.de/sneak/webhooker/pkg/config"
 	"go.uber.org/fx"
+	"sneak.berlin/go/webhooker/internal/globals"
+	"sneak.berlin/go/webhooker/internal/logger"
+	pkgconfig "sneak.berlin/go/webhooker/pkg/config"
 
 	// spooky action at a distance!
 	// this populates the environment

internal/config/config_test.go

@@ -4,14 +4,14 @@ import (
 	"os"
 	"testing"
 
-	"git.eeqj.de/sneak/webhooker/internal/globals"
-	"git.eeqj.de/sneak/webhooker/internal/logger"
-	pkgconfig "git.eeqj.de/sneak/webhooker/pkg/config"
 	"github.com/spf13/afero"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 	"go.uber.org/fx"
 	"go.uber.org/fx/fxtest"
+	"sneak.berlin/go/webhooker/internal/globals"
+	"sneak.berlin/go/webhooker/internal/logger"
+	pkgconfig "sneak.berlin/go/webhooker/pkg/config"
 )
 
 // createTestConfig creates a test configuration file in memory