feat(otel): export logs through the tracing pipeline, correlated with traces (#147)

Logs were a separate pipeline: env_logger in debug (never exported) and
opentelemetry-appender-log in release (exported without trace context,
so SigNoz could not link logs to traces).

- tracing-subscriber `tracing-log` feature: try_init installs LogTracer,
  so log:: records become tracing events: one console format, and
  RUST_LOG per-module directives still apply to them.
- opentelemetry-appender-tracing exports events as OTel log records when
  OTLP_OTLS_ENDPOINT is set (any build), stamped with the enclosing
  span's trace_id/span_id. A per-layer filter drops the exporter's own
  crates.
- The OTel span layer keeps only WARN/ERROR events as span events; the
  info/debug copies duplicated the correlated logs.
- Remove env_logger init in the server, init_logs, and the unused
  opentelemetry-appender-log / opentelemetry-stdout deps.
- tests/otel_log_correlation.rs pins correlation (native + bridged),
  the span-event filter, and per-module filtering of bridged records.
- Constitution 1.2.0 (Principle V logging rule), CLAUDE.md, README,
  .env.example.

Closes #147

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -73,8 +73,8 @@ They should be defined where the binary is located or above it in an `.env` file
 - `BIND_URL` is the url and port to bind to (typically your own IP address)
 - `LOCAL_BIND_URL` (optional) is a second, loopback listener [default: `localhost:8088`]. Set it to an empty string to skip it, e.g. to run a second instance such as the `dev/e2e` harness alongside one that already owns 8088
 - `SECRET_KEY` is the *hopefully* random string to sign Tokens with
-- `RUST_LOG` is one of `off, error, warn, info, debug, trace`, from least to most noisy [default: `info` for spans, `error` for dev console logs]. It also gates tracing-span export, so keep it at `info` or `debug`
-- `OTLP_OTLS_ENDPOINT` (optional) is an OTLP/gRPC collector URL (e.g. SigNoz, Jaeger) for span export, in any build [default: unset, no export]
+- `RUST_LOG` is one of `off, error, warn, info, debug, trace`, from least to most noisy [default: `info`]. It gates console output, span export and log export alike, so keep it at `info` or `debug`
+- `OTLP_OTLS_ENDPOINT` (optional) is an OTLP/gRPC collector URL (e.g. SigNoz, Jaeger) for span and log export (logs carry trace ids, so they link to traces), in any build [default: unset, no export]
 - `EXCLUDED_DIRS` is a comma separated list of directories to exclude from the Memories API
 - `PREVIEW_CLIPS_DIRECTORY` (optional) is a path where generated video preview clips should be stored [default: `preview_clips`]
 - `WATCH_QUICK_INTERVAL_SECONDS` (optional) is the interval in seconds for quick file scans [default: 60]