chore: consolidate DBURL into DATA_DIR, codebase audit for 1.0.0

DBURL → DATA_DIR consolidation:
- Remove DBURL env var entirely; main DB now lives at {DATA_DIR}/webhooker.db
- database.go constructs DB path from config.DataDir, ensures dir exists
- Update DATA_DIR prod default from /data/events to /data
- Update all tests to use DataDir instead of DBURL
- Update Dockerfile: /data (not /data/events) for all SQLite databases
- Update README configuration table, Docker examples, architecture docs

Dead code removal:
- Remove unused IndexResponse struct (handlers/index.go)
- Remove unused TemplateData struct (handlers/handlers.go)

Stale comment cleanup:
- Remove TODO in server.go (DB cleanup handled by fx lifecycle)
- Fix nolint:golint → nolint:revive on ServerParams for consistency
- Clean up verbose middleware/routing comments in routes.go
- Fix TODO fan-out description (worker pool, not goroutine-per-target)

.gitignore fixes:
- Add data/ directory to gitignore
- Remove stale config.yaml entry (env-only config since rework)

internal/handlers/handlers.go

@@ -99,14 +99,6 @@ func (s *Handlers) decodeJSON(w http.ResponseWriter, r *http.Request, v interfac
 	return json.NewDecoder(r.Body).Decode(v)
 }
 
-// TemplateData represents the common data passed to templates
-type TemplateData struct {
-	User      *UserInfo
-	Version   string
-	UserCount int64
-	Uptime    string
-}
-
 // UserInfo represents user information for templates
 type UserInfo struct {
 	ID       string

internal/handlers/handlers_test.go

@@ -34,7 +34,6 @@ func TestHandleIndex(t *testing.T) {
 			logger.New,
 			func() *config.Config {
 				return &config.Config{
-					DBURL:   "file:" + t.TempDir() + "/test.db?cache=shared&mode=rwc",
 					DataDir: t.TempDir(),
 				}
 			},
@@ -66,7 +65,6 @@ func TestRenderTemplate(t *testing.T) {
 			logger.New,
 			func() *config.Config {
 				return &config.Config{
-					DBURL:   "file:" + t.TempDir() + "/test.db?cache=shared&mode=rwc",
 					DataDir: t.TempDir(),
 				}
 			},

internal/handlers/index.go

@@ -8,11 +8,6 @@ import (
 	"sneak.berlin/go/webhooker/internal/database"
 )
 
-type IndexResponse struct {
-	Message string `json:"message"`
-	Version string `json:"version"`
-}
-
 func (s *Handlers) HandleIndex() http.HandlerFunc {
 	// Calculate server start time
 	startTime := time.Now()