refactor(log): split location into package/file/class/method, auto-derived

Per the log schema: 'package' is the Go package (absent on
Python-emitted lines), 'file' the Go/Python source basename, 'class' the
Go receiver or Python class (omitted when there is none -- free
functions no longer masquerade under a package-as-class), 'method' the
emitting function. applog.App() now takes no arguments and derives all
of it from runtime.Caller, so labels can never drift from the code; the
manual http/wrapper emitters and forwarded wrapper.py lines (file=
wrapper.py, no package) carry the same fields.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

backend/cmd/dumpschema/main.go

@@ -93,12 +93,12 @@ func main() {
 
 	outPath := "../docs/DATABASE.md"
 	must(os.WriteFile(outPath, []byte(b.String()), 0644))
-	applog.App("main", "main").Info("wrote schema doc", "path", outPath)
+	applog.App().Info("wrote schema doc", "path", outPath)
 }
 
 func must(err error) {
 	if err != nil {
-		applog.App("main", "must").Error("dumpschema failed", "error", err)
+		applog.App().Error("dumpschema failed", "error", err)
 		os.Exit(1)
 	}
 }

backend/cmd/geniusrund/main.go

@@ -24,7 +24,7 @@ import (
 // structured replacement for log.Fatalf, so even startup failures come
 // out as JSON lines.
 func fatal(msg string, err error) {
-	applog.App("main", "fatal").Error(msg, "error", err)
+	applog.App().Error(msg, "error", err)
 	os.Exit(1)
 }
 
@@ -103,17 +103,17 @@ func main() {
 
 	httpServer := &http.Server{Addr: envCfg.BackendAddr, Handler: server.Router()}
 	go func() {
-		applog.App("main", "main").Info("geniusrund listening", "addr", envCfg.BackendAddr)
+		applog.App().Info("geniusrund listening", "addr", envCfg.BackendAddr)
 		if err := httpServer.ListenAndServe(); err != nil && err != http.ErrServerClosed {
 			fatal("http server", err)
 		}
 	}()
 
 	<-ctx.Done()
-	applog.App("main", "main").Info("shutting down")
+	applog.App().Info("shutting down")
 	shutdownCtx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
 	defer cancel()
 	if err := httpServer.Shutdown(shutdownCtx); err != nil {
-		applog.App("main", "main").Error("http server shutdown", "error", err)
+		applog.App().Error("http server shutdown", "error", err)
 	}
 }

backend/cmd/seedsample/main.go

@@ -243,7 +243,7 @@ func must(err error) {
 // fatal logs through the application JSON logger and exits -- the
 // structured replacement for log.Fatal.
 func fatal(msg string, err error) {
-	applog.App("main", "fatal").Error(msg, "error", err)
+	applog.App().Error(msg, "error", err)
 	os.Exit(1)
 }
 
@@ -255,7 +255,7 @@ func mustFindKindID(ctx context.Context, db *store.DB, userID int64, name string
 			return k.ID
 		}
 	}
-	applog.App("main", "mustFindKindID").Error("no workout kind with that name for the seeded user (did ProvisionUser seed the taxonomy?)", "kind", name)
+	applog.App().Error("no workout kind with that name for the seeded user (did ProvisionUser seed the taxonomy?)", "kind", name)
 	os.Exit(1)
 	return 0
 }