feat(core): edit icon in navigation panel (#13595)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

- **New Features**
- Rename dialog now edits per-item explorer icons (emoji or custom) and
can skip name-change callbacks. Doc icon picker added to the editor with
localized "Add icon" placeholder and readonly rendering. Icon editor
supports fallbacks, trigger variants, and improved input/test-id wiring.

- **Style**
- Updated icon picker and trigger sizing and placeholder visuals;
title/icon layout adjustments.

- **Chores**
- Explorer icon storage and module added to persist and serve icons
across the app.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

blocksuite/affine/fragments/doc-title/src/doc-title.ts

@@ -19,6 +19,7 @@ const DOC_BLOCK_CHILD_PADDING = 24;
 
 export class DocTitle extends WithDisposable(ShadowlessElement) {
   static override styles = css`
+    .doc-icon-container,
     .doc-title-container {
       box-sizing: border-box;
       font-family: var(--affine-font-family);
@@ -49,6 +50,7 @@ export class DocTitle extends WithDisposable(ShadowlessElement) {
 
     /* Extra small devices (phones, 640px and down) */
     @container viewport (width <= 640px) {
+      .doc-icon-container,
       .doc-title-container {
         padding-left: ${DOC_BLOCK_CHILD_PADDING}px;
         padding-right: ${DOC_BLOCK_CHILD_PADDING}px;