feat: multi-component-selector (#1728)

<!-- This is an auto-generated description by cubic. -->
## Summary by cubic
Adds multi-component selection in the preview and sends all selected
components to chat for targeted edits. Updates overlays, UI, and IPC to
support arrays, smarter context focusing, and cross-platform path
normalization.

- **New Features**
- Select multiple components in the iframe; selection mode stays active
until you deactivate it.
- Show a scrollable list of selections with remove buttons and a Clear
all; remove from the list or click an overlay in the preview to
deselect. Sending clears all overlays.
- Separate hover vs selected overlays with labels on hover; overlays
persist after deactivation and re-position on layout changes/resizes.
- Chat input and streaming now send selectedComponents; server builds
per-component snippets and focuses their files in smart context.

- **Migration**
- Replace selectedComponentPreviewAtom with
selectedComponentsPreviewAtom (ComponentSelection[]).
- ChatStreamParams now uses selectedComponents; migrate any
single-selection usages.
  - previewIframeRefAtom added for clearing overlays from the parent.

<sup>Written for commit da0d64cc9e9f83fbf4b975278f6c869f0d3a8c7d.
Summary will update automatically on new commits.</sup>

<!-- End of auto-generated description by cubic. -->

e2e-tests/helpers/test_helper.ts

@@ -522,8 +522,15 @@ export class PageObject {
       .click({ timeout: Timeout.EXTRA_LONG });
   }
 
-  async clickDeselectComponent() {
-    await this.page.getByRole("button", { name: "Deselect component" }).click();
+  async clickDeselectComponent(options?: { index?: number }) {
+    const buttons = this.page.getByRole("button", {
+      name: "Deselect component",
+    });
+    if (options?.index !== undefined) {
+      await buttons.nth(options.index).click();
+    } else {
+      await buttons.first().click();
+    }
   }
 
   async clickPreviewMoreOptions() {
@@ -582,12 +589,12 @@ export class PageObject {
     await expect(this.getChatInputContainer()).toMatchAriaSnapshot();
   }
 
-  getSelectedComponentDisplay() {
+  getSelectedComponentsDisplay() {
     return this.page.getByTestId("selected-component-display");
   }
 
-  async snapshotSelectedComponentDisplay() {
-    await expect(this.getSelectedComponentDisplay()).toMatchAriaSnapshot();
+  async snapshotSelectedComponentsDisplay() {
+    await expect(this.getSelectedComponentsDisplay()).toMatchAriaSnapshot();
   }
 
   async snapshotPreview({ name }: { name?: string } = {}) {