feat(observability): add OpenTelemetry request tracing

- Add opt-in OTLP/HTTP export with bounded background batching.
- Propagate W3C context and correlate wide events with response trace IDs.
- Update my_helpers for Convex child spans and native request IDs.
- Respect parent sampling and shut down the exporter off the event loop.
- Keep raw URLs, payloads and exception text out of spans.
- Cover worker isolation, retries, sampling, privacy and exporter lifecycle.
- Document collector configuration and bump NanoShare to 1.27.5.
- Refresh locked dependencies, including pytest and watchdog.
- Validate the changes with 293 passing tests.

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "nanoshare"
-version = "1.27.4"
+version = "1.27.5"
 description = "Add your description here"
 readme = "README.md"
 requires-python = ">=3.15"
@@ -12,6 +12,8 @@ dependencies = [
     "httpx>=0.28.1",
     "hypercorn>=0.18.0",
     "joserfc>=1.6.5",
+    "opentelemetry-exporter-otlp-proto-http>=1.45.1",
+    "opentelemetry-sdk>=1.45.1",
     "python-dotenv>=1.2.2",
     "quart>=0.20.0",
     "quart-flask-patch>=0.3.1",