refactor(log): unified schema — mandatory type/class/method, request_id removed

Every log record now carries type ('http' for the request middleware
line, 'wrapper' for garmin execute() calls and forwarded wrapper.py
stderr, 'app' for everything else), class (Go type with package, or the
package/module for free functions), and method (the emitting Go/Python
function -- wrapper.py stamps it automatically, so its msg prefixes are
gone). msg is optional and omitted when empty; the redundant messages
('HTTP request', 'wrapper call', 'garmin wrapper stderr') are dropped,
the HTTP verb moves to http_method, source=garmin-wrapper is replaced by
type=wrapper, and the request_id middleware plumbing (applog
WithLogger/FromContext) is removed. applog.App(class, method) is the
tagging helper for app records.

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

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) {
-	slog.Error(msg, "error", err)
+	applog.App("main", "fatal").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
 		}
 	}
-	slog.Error("no workout kind with that name for the seeded user (did ProvisionUser seed the taxonomy?)", "kind", name)
+	applog.App("main", "mustFindKindID").Error("no workout kind with that name for the seeded user (did ProvisionUser seed the taxonomy?)", "kind", name)
 	os.Exit(1)
 	return 0
 }