docs: consolidate design documentation and standardize crate English

crates/plugin-pdk/tests/fixtures/component-tool-source.txt

@@ -0,0 +1,38 @@
+//! Minimal Component Model Tool plugin authoring sketch using `yoi-plugin-pdk`.
+//!
+//! Build this as a `wasm32-unknown-unknown` cdylib with Component Model tooling
+//! and package the adapted component as `plugin.component.wasm`.
+
+use serde::{Deserialize, Serialize};
+use yoi_plugin_pdk::wit_bindgen;
+use yoi_plugin_pdk::{ToolContext, ToolError, ToolOutput};
+
+wit_bindgen::generate!({
+    world: "tool",
+    path: "../../../resources/plugin/wit",
+    generate_all,
+    runtime_path: "yoi_plugin_pdk::wit_bindgen::rt",
+});
+
+#[derive(Debug, Deserialize)]
+struct EchoInput {
+    text: String,
+}
+
+#[derive(Debug, Serialize)]
+struct EchoOutput<'a> {
+    tool: &'a str,
+    text: String,
+}
+
+fn handle_echo(ctx: ToolContext, input: EchoInput) -> Result<ToolOutput, ToolError> {
+    ToolOutput::json(
+        format!("{} ok", ctx.tool_name()),
+        EchoOutput {
+            tool: ctx.tool_name(),
+            text: input.text,
+        },
+    )
+}
+
+yoi_plugin_pdk::export_component_tool!(Plugin, handle_echo);