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>

Cargo.lock

@@ -2107,9 +2107,8 @@ dependencies = [
  "libsqlite3-sys",
  "log",
  "opentelemetry",
- "opentelemetry-appender-log",
+ "opentelemetry-appender-tracing",
  "opentelemetry-otlp",
- "opentelemetry-stdout",
  "opentelemetry_sdk",
  "path-absolutize",
  "prometheus",
@@ -2125,6 +2124,7 @@ dependencies = [
  "tokio-util",
  "tracing",
  "tracing-actix-web",
+ "tracing-log",
  "tracing-opentelemetry",
  "tracing-subscriber",
  "tzf-rs",
@@ -2759,13 +2759,17 @@ dependencies = [
 ]
 
 [[package]]
-name = "opentelemetry-appender-log"
-version = "0.31.0"
+name = "opentelemetry-appender-tracing"
+version = "0.31.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "9e50c59a96bd6a723a4329c5db31eb04fa4488c5f141ae7b9d4fd587439e6ee1"
+checksum = "ef6a1ac5ca3accf562b8c306fa8483c85f4390f768185ab775f242f7fe8fdcc2"
 dependencies = [
- "log",
  "opentelemetry",
+ "tracing",
+ "tracing-core",
+ "tracing-log",
+ "tracing-opentelemetry",
+ "tracing-subscriber",
 ]
 
 [[package]]
@@ -2813,17 +2817,6 @@ dependencies = [
  "tonic-prost",
 ]
 
-[[package]]
-name = "opentelemetry-stdout"
-version = "0.31.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "bc8887887e169414f637b18751487cce4e095be787d23fad13c454e2fb1b3811"
-dependencies = [
- "chrono",
- "opentelemetry",
- "opentelemetry_sdk",
-]
-
 [[package]]
 name = "opentelemetry_sdk"
 version = "0.31.0"
@@ -4443,6 +4436,7 @@ dependencies = [
  "thread_local",
  "tracing",
  "tracing-core",
+ "tracing-log",
 ]
 
 [[package]]