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/internal/garmin/wrapper/wrapper.py

@@ -31,7 +31,7 @@ def _log(level, msg, **attrs):
     never print free text to stderr or stdout from this process (stdout is
     reserved for the request/response protocol). The emitting function is
     stamped as "method" automatically; the Go side adds the rest of the
-    log schema (type=wrapper, class=wrapper)."""
+    log schema (type=wrapper, file=wrapper.py)."""
     entry = {"level": level, "msg": msg, "method": sys._getframe(1).f_code.co_name}
     entry.update(attrs)
     print(json.dumps(entry), file=sys.stderr, flush=True)