feat(preview): inline video player via vidstack + hover-warm prefetch

Replace PreviewOverlay's bare <video controls> with a vidstack-driven
player wrapping the same source URL. Vidstack's default video layout
provides a polished chrome (gradient bottom bar, large play overlay,
hover-revealed scrubber) and registers <media-player>/<media-provider>
custom elements that vendor the browser quirks.

To keep first-frame latency low, PhotoTile starts a hover-warm fetch
of the playback URL after a short (120 ms) delay — a single Range
request of the first 512 KB pages the backend's pre-transcoded MP4
cache file into the OS page cache and lands in the browser's HTTP
cache, so when the player mounts and issues its own bytes=0- request
the response is satisfied from disk. Each hash is warmed at most once
per session; AbortController cancels hovers that don't commit.

The vidstack modules are dynamically imported on mount so they never
run during SvelteKit's static prerender — they side-effect
customElements.define() calls which would crash under SSR.

web/package-lock.json

@@ -18,7 +18,8 @@
 				"mode-watcher": "^1.1.0",
 				"svelte-sonner": "^1.1.1",
 				"tailwind-merge": "^3.6.0",
-				"tailwind-variants": "^3.2.2"
+				"tailwind-variants": "^3.2.2",
+				"vidstack": "^1.12.13"
 			},
 			"devDependencies": {
 				"@sveltejs/adapter-static": "^3.0.10",
@@ -1835,6 +1836,15 @@
 				"url": "https://opencollective.com/parcel"
 			}
 		},
+		"node_modules/lit-html": {
+			"version": "2.8.0",
+			"resolved": "https://registry.npmjs.org/lit-html/-/lit-html-2.8.0.tgz",
+			"integrity": "sha512-o9t+MQM3P4y7M7yNzqAyjp7z+mQGa4NS4CxiyLqFPyFWyc4O+nodLrkrxSaCTrla6M5YOLaT3RpbbqjszB5g3Q==",
+			"license": "BSD-3-Clause",
+			"dependencies": {
+				"@types/trusted-types": "^2.0.2"
+			}
+		},
 		"node_modules/locate-character": {
 			"version": "3.0.0",
 			"resolved": "https://registry.npmjs.org/locate-character/-/locate-character-3.0.0.tgz",
@@ -1912,6 +1922,15 @@
 				"node": ">= 0.4"
 			}
 		},
+		"node_modules/media-captions": {
+			"version": "1.0.4",
+			"resolved": "https://registry.npmjs.org/media-captions/-/media-captions-1.0.4.tgz",
+			"integrity": "sha512-cyDNmuZvvO4H27rcBq2Eudxo9IZRDCOX/I7VEyqbxsEiD2Ei7UYUhG/Sc5fvMZjmathgz3fEK7iAKqvpY+Ux1w==",
+			"license": "MIT",
+			"engines": {
+				"node": ">=16"
+			}
+		},
 		"node_modules/mime-db": {
 			"version": "1.52.0",
 			"resolved": "https://registry.npmjs.org/mime-db/-/mime-db-1.52.0.tgz",
@@ -2513,6 +2532,34 @@
 			"dev": true,
 			"license": "MIT"
 		},
+		"node_modules/unplugin": {
+			"version": "1.16.1",
+			"resolved": "https://registry.npmjs.org/unplugin/-/unplugin-1.16.1.tgz",
+			"integrity": "sha512-4/u/j4FrCKdi17jaxuJA0jClGxB1AvU2hw/IuayPc4ay1XGaJs/rbb4v5WKwAjNifjmXK9PIFyuPiaK8azyR9w==",
+			"license": "MIT",
+			"dependencies": {
+				"acorn": "^8.14.0",
+				"webpack-virtual-modules": "^0.6.2"
+			},
+			"engines": {
+				"node": ">=14.0.0"
+			}
+		},
+		"node_modules/vidstack": {
+			"version": "1.12.13",
+			"resolved": "https://registry.npmjs.org/vidstack/-/vidstack-1.12.13.tgz",
+			"integrity": "sha512-vuNeyRmWoH/7EoFVDYjp9nkgcqtCMmal518LDeb78dYKgWb+p6+vtY0AzDhrkBv5q1UiCn+xwmjMmwvSlPLuhQ==",
+			"license": "MIT",
+			"dependencies": {
+				"@floating-ui/dom": "^1.6.10",
+				"lit-html": "^2.8.0",
+				"media-captions": "^1.0.4",
+				"unplugin": "^1.12.0"
+			},
+			"engines": {
+				"node": ">=18"
+			}
+		},
 		"node_modules/vite": {
 			"version": "8.0.13",
 			"resolved": "https://registry.npmjs.org/vite/-/vite-8.0.13.tgz",
@@ -2611,6 +2658,12 @@
 				}
 			}
 		},
+		"node_modules/webpack-virtual-modules": {
+			"version": "0.6.2",
+			"resolved": "https://registry.npmjs.org/webpack-virtual-modules/-/webpack-virtual-modules-0.6.2.tgz",
+			"integrity": "sha512-66/V2i5hQanC51vBQKPH4aI8NMAcBW59FVBs+rC7eGHupMyfn34q7rZIE+ETlJ+XTevqfUhVVBgSUNSW2flEUQ==",
+			"license": "MIT"
+		},
 		"node_modules/zimmerframe": {
 			"version": "1.1.4",
 			"resolved": "https://registry.npmjs.org/zimmerframe/-/zimmerframe-1.1.4.tgz",