feat(observability): add structured application logging

Emit correlated JSON logs from the API and FunASR services, propagate request IDs to the client, and configure bounded opt-in Docker logging.

Document the host-wide Grafana/Loki query workflow and keep observability deployment ownership outside the application repository.

server/Cargo.lock

@@ -1890,7 +1890,7 @@ dependencies = [
 
 [[package]]
 name = "teaching-feedback-api"
-version = "0.1.0"
+version = "0.2.0"
 dependencies = [
  "axum",
  "base64",
@@ -1906,6 +1906,7 @@ dependencies = [
  "sqlx",
  "thiserror",
  "tokio",
+ "tower",
  "tower-http",
  "tracing",
  "tracing-subscriber",
@@ -2051,6 +2052,7 @@ dependencies = [
  "tower-service",
  "tracing",
  "url",
+ "uuid",
 ]
 
 [[package]]
@@ -2109,6 +2111,16 @@ dependencies = [
  "tracing-core",
 ]
 
+[[package]]
+name = "tracing-serde"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "704b1aeb7be0d0a84fc9828cae51dab5970fee5088f83d1dd7ee6f6246fc6ff1"
+dependencies = [
+ "serde",
+ "tracing-core",
+]
+
 [[package]]
 name = "tracing-subscriber"
 version = "0.3.23"
@@ -2119,12 +2131,15 @@ dependencies = [
  "nu-ansi-term",
  "once_cell",
  "regex-automata",
+ "serde",
+ "serde_json",
  "sharded-slab",
  "smallvec",
  "thread_local",
  "tracing",
  "tracing-core",
  "tracing-log",
+ "tracing-serde",
 ]
 
 [[package]]