Add vitepress docs

docs/app/collection.md

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+# Collection Stores
+
+The `collection` utility creates stores that handle caching, loading, and indexing of Nostr data. It provides a consistent pattern for managing entities that need to be fetched from the network and cached locally.
+
+```typescript
+const {
+  indexStore,    // Map of all items by key
+  deriveItem,    // Get reactive item by key
+  loadItem       // Trigger network load
+} = collection({
+  name: "storeName",      // For persistence
+  store: writable([]),    // Base store
+  getKey: item => item.id // How to index items
+  load: async (key) => {  // Network loader
+    // Load logic here
+  }
+})
+```
+
+## Available Collections
+
+```typescript
+// Profiles
+profiles → profilesByPubkey → deriveProfile → loadProfile
+
+// Lists
+follows → followsByPubkey → deriveFollows → loadFollows
+mutes → mutesByPubkey → deriveMutes → loadMutes
+pins → pinsByPubkey → derivePins → loadPins
+
+// Relays
+relays → relaysByUrl → deriveRelay → loadRelay
+relaySelections → relaySelectionsByPubkey → deriveRelaySelections → loadRelaySelections
+inboxRelaySelections → inboxRelaySelectionsByPubkey → deriveInboxRelaySelections → loadInboxRelaySelections
+
+// Identity
+handles → handlesByNip05 → deriveHandle → loadHandle
+zappers → zappersByLnurl → deriveZapper → loadZapper
+```
+
+## Real World Examples
+
+### Loading and Displaying Profiles
+
+```typescript
+import {
+  deriveProfile,
+  loadProfile,
+  displayProfile
+} from '@welshman/app'
+
+// In a Svelte component
+let profile
+
+// Subscribe to profile changes
+$: profile = $deriveProfile(pubkey)
+
+// Load automatically triggers when needed
+onMount(() => {
+  loadProfile(pubkey, {
+    // Optional request params
+    relays: ["wss://relay.example.com"]
+  })
+})
+
+// Display with fallback
+$: name = displayProfile(profile, "unknown")
+```
+
+### Managing Relay Selections
+
+```typescript
+import {
+  deriveRelaySelections,
+  loadRelaySelections,
+  getReadRelayUrls,
+  getWriteRelayUrls
+} from '@welshman/app'
+
+// Get user's relay preferences
+const selections = deriveRelaySelections(pubkey).get()
+
+// Load from network if needed
+await loadRelaySelections(pubkey)
+
+// Get read/write URLs
+const readRelays = getReadRelayUrls(selections)
+const writeRelays = getWriteRelayUrls(selections)
+
+// Use with router
+const relays = ctx.app.router
+  .FromPubkey(pubkey)
+  .getUrls()
+```
+
+Each collection automatically:
+- Caches to IndexedDB
+- Deduplicates network requests
+- Updates reactively
+- Provides typed access
+- Handles loading states
+
+The pattern is consistent across all stores, making it predictable to work with different types of nostr data.