feat:video player, like button, and media fallbacks

Add VideoPlayer and LikeButton components with optimistic UI and /server
endpoints for likes. Update media processor to emit WebP and JPEG
fallbacks, store fallback URLs in the DB (migration + snapshot), add
video placeholder asset, and relax CSP media-src for R2.

drizzle/meta/_journal.json

@@ -29,6 +29,13 @@
       "when": 1760092217884,
       "tag": "0003_woozy_lily_hollister",
       "breakpoints": true
+    },
+    {
+      "idx": 4,
+      "version": "7",
+      "when": 1760456880877,
+      "tag": "0004_large_doctor_strange",
+      "breakpoints": true
     }
   ]
 }