fix search modal race condition and add 304 support for images

Route all search modal open/close through the JS hook via custom DOM
events so the _closing flag is always correctly managed. Prevents the
modal flashing back after Escape when a search response is in flight.

Add If-None-Match / 304 Not Modified handling to the image controller
so browsers don't re-download images on revalidation.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

assets/js/app.js

@@ -341,6 +341,9 @@ const SearchModal = {
     }
     document.addEventListener("keydown", this._globalKeydown)
 
+    this.el.addEventListener("open-search", () => this.open())
+    this.el.addEventListener("close-search", () => this.close())
+
     this.el.addEventListener("keydown", (e) => {
       if (!this.isOpen()) return
 
@@ -370,6 +373,7 @@ const SearchModal = {
   },
 
   updated() {
+    if (this._closing) this.el.style.display = "none"
     this.selectedIndex = -1
     this.updateHighlight()
   },
@@ -379,6 +383,7 @@ const SearchModal = {
   },
 
   open() {
+    this._closing = false
     this.el.style.display = "flex"
     this.pushEvent("open_search", {})
     const input = this.el.querySelector("#search-input")
@@ -391,6 +396,7 @@ const SearchModal = {
   },
 
   close() {
+    this._closing = true
     this.el.style.display = "none"
     this.pushEvent("clear_search", {})
     this.selectedIndex = -1