docs: add hands-on Cordis tutorial

Seven-chapter tutorial under docs/cordis-tutorial/ for agent developers
new to Cordis: first plugin, lifecycle/effects, services, events,
config, composition/HMR, and a final chapter registering a tool against
real harness services. Every transcript was produced by running the
chapter files in a gitignored tmp/ scratch directory.

Published to both website locales as mirrored English pages under a new
'Cordis tutorial' develop-sidebar section; a Chinese pair can be added
later without route changes.

docs/cordis-tutorial/02-lifecycle-and-effects.md

@@ -0,0 +1,89 @@
+# 2. Lifecycle and effects
+
+A Cordis plugin can be unloaded by a config edit, hot reload, explicit disposal, or loss of a required service. Registrations made through Cordis APIs are effects and are undone when their owning plugin unloads; resources managed outside those APIs must be wrapped in `ctx.effect()`.
+
+## Effects
+
+For a resource Cordis does not already manage — a timer, a connection, a watcher — wrap it in `ctx.effect()` and return a disposer:
+
+Create `lifecycle.ts` in `tmp/cordis-tutorial`:
+
+```ts
+import type { Context } from 'cordis'
+
+export const name = 'lifecycle-demo'
+
+function heartbeat(ctx: Context) {
+  console.log('heartbeat plugin loading')
+  ctx.effect(() => {
+    const timer = setInterval(() => console.log('tick'), 200)
+    return () => {
+      clearInterval(timer)
+      console.log('heartbeat cleaned up')
+    }
+  })
+}
+
+export function apply(ctx: Context) {
+  // Mount a child plugin and keep its fiber to dispose it later.
+  const fiber = ctx.plugin(heartbeat)
+  setTimeout(async () => {
+    await fiber.dispose()
+    console.log('disposed')
+    process.exit(0)
+  }, 700)
+}
+```
+
+Point `cordis.yml` at it:
+
+```yaml
+- name: './lifecycle.ts'
+```
+
+Run (`node --import tsx ../../vendor/cordis/bin.js`) and you get:
+
+```
+heartbeat plugin loading
+tick
+tick
+tick
+heartbeat cleaned up
+disposed
+```
+
+Three things to notice:
+
+- `ctx.plugin(heartbeat)` mounts a plugin **from code** — the same operation the YAML loader performs for each config entry. It returns a **fiber**, the runtime handle for one loaded plugin instance.
+- The effect body runs during load; the disposer it returns runs during unload. You never call the disposer yourself for a plugin-lifetime resource.
+- `fiber.dispose()` resolves after all of the plugin's cleanup — including async disposers — has finished, and recursively unloads any child plugins it mounted.
+
+## The fiber state machine
+
+Every loaded plugin instance owns a fiber that moves through these states:
+
+```
+PENDING → LOADING → ACTIVE → UNLOADING → DISPOSED
+                 ↘ FAILED
+```
+
+- **PENDING** — declared, but a required service (chapter 3) is not available yet.
+- **LOADING / ACTIVE** — `apply` is running / has completed.
+- **FAILED** — `apply` or config validation threw.
+- **UNLOADING / DISPOSED** — disposers are running / everything is torn down.
+
+You will meet PENDING again in [chapter 6](06-composition-and-hmr.md), where it is the usual answer to "why does my plugin print nothing?".
+
+## What is already an effect
+
+You rarely write `ctx.effect()` yourself, because the built-in registration APIs are effects already:
+
+- `ctx.on(event, listener)` — the listener is removed on unload ([chapter 4](04-events.md)).
+- `ctx.plugin(child)` — the child is disposed with its parent.
+- Service registrations are effects. Harness registries such as `ctx.tools.register(...)` also attach their returned disposers to the calling plugin, so they unwind automatically ([chapter 7](07-into-the-harness.md)).
+
+For a resource Cordis does not manage, acquire it inside `ctx.effect()` and return a disposer that releases it. Cordis then invokes that release during unloading, including hot reload.
+
+One ordering caveat: disposers start in reverse registration order, but multiple **async** disposers run concurrently. If teardown steps must run in sequence, keep them in one disposer and await them there.
+
+Next: [Services](03-services.md) — how plugins share capabilities.