Add vitepress docs

docs/app/thunks.md

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+# Thunks
+
+Thunks provide optimistic updates for event publishing. They immediately update the local repository while handling the actual signing and publishing asynchronously, making the UI feel more responsive.
+
+## Overview
+
+A thunk:
+- Updates local state immediately
+- Handles event signing in the background
+- Manages publish status per relay
+- Supports soft-undo via abort
+- Can be delayed/cancelled
+- Tracks successful publishes
+
+## Basic Usage
+
+```typescript
+import {publishThunk} from '@welshman/app'
+import {createEvent, NOTE} from '@welshman/util'
+
+const publish = async (content: string) => {
+  // Get optimal relays for publishing
+  const relays = ctx.app.router
+    .FromUser()
+    .getUrls()
+
+  // Create and publish thunk
+  const thunk = await publishThunk({
+    event: createEvent(NOTE, {content}),
+    relays,
+    delay: 3000, // 3s window for abort
+  })
+
+  // Track publish status
+  thunk.status.subscribe(statuses => {
+    for (const [url, {status, message}] of Object.entries(statuses)) {
+      console.log(`${url}: ${status} ${message}`)
+    }
+  })
+
+  // Can abort within delay window
+  setTimeout(() => {
+    if (userWantsToCancel) {
+      thunk.controller.abort()
+    }
+  }, 1000)
+
+  // Wait for completion
+  const results = await thunk.result
+  return results
+}
+```