Say "structured content", not "structured output"

The spec never uses the phrase "structured output". It defines two separate
things under Tool Result: "Structured Content" (the `structuredContent` field)
and "Output Schema" (the `outputSchema` field). Collapsing them into
"structured output" conflates the two.

It is also actively confusing here. In LLM tooling "structured output" means
constrained decoding — making the *model* emit conforming JSON. These clients
call a model API, so a reader could reasonably take the phrase to mean the
tool constrains the model's response, which is the opposite of what is going
on: the tool describes the shape of its own result.

Headings and prose now say "structured content". References to real
identifiers are left alone: the Python SDK's own docs page is called
Structured Output and lives at docs/servers/structured-output.md, and its
decorator parameter is `structured_output`.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

weather-server-rust/src/main.rs

@@ -68,7 +68,7 @@ struct ForecastPeriod {
     detailed_forecast: String,
 }
 
-/// One element of `get_alerts`' structured output. Declaring `Vec<Alert>` as
+/// One element of `get_alerts`' structured content. Declaring `Vec<Alert>` as
 /// the output schema makes `structuredContent` a top-level JSON array rather
 /// than an object wrapping one, which revision 2026-07-28 is the first to allow.
 #[derive(Debug, Serialize, JsonSchema)]
@@ -85,7 +85,7 @@ pub struct Alert {
     instructions: String,
 }
 
-/// `get_forecast`' structured output: the object case.
+/// `get_forecast`' structured content: the object case.
 #[derive(Debug, Serialize, JsonSchema)]
 pub struct Forecast {
     /// Latitude the forecast is for.