feat: F5.5 large binary files as blobs on server F

From 16 KB a picture's or binary file's entry names its bytes by their
SHA-256 instead of holding them; the bytes are on F, content-addressed
(GET/POST /blobs with the session's grant, from the editor's origin, at
most 16 MiB). A document's blob side says where they are: the editor's
fetches and uploads, the room thread's asks F's main thread, and a start
waits for the ones asked for; without a side everything stays in the
document. Text stays Y.Text. A blob whose bytes are not there is never
written back empty. A blob F has not got yet is asked for again a few
times, and a running room reads late bytes.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

package-lock.json

@@ -895,6 +895,18 @@
         "node": "^22.20 || ^24.12 || >=25"
       }
     },
+    "node_modules/@noble/hashes": {
+      "version": "2.4.0",
+      "resolved": "https://registry.npmjs.org/@noble/hashes/-/hashes-2.4.0.tgz",
+      "integrity": "sha512-X5XaVWZIBCT7HHZGm5I7ZQXDwLG+bGXuSrMQAW+7Zvl87h1kmc1ZB1VSRJcpUfoUrGQp4Fkoxm5kZ+Ms+aW+eA==",
+      "license": "MIT",
+      "engines": {
+        "node": ">= 20.19.0"
+      },
+      "funding": {
+        "url": "https://paulmillr.com/funding/"
+      }
+    },
     "node_modules/@pdf-lib/standard-fonts": {
       "version": "1.0.0",
       "resolved": "https://registry.npmjs.org/@pdf-lib/standard-fonts/-/standard-fonts-1.0.0.tgz",
@@ -2843,6 +2855,7 @@
       "dependencies": {
         "@mdg-filius/core": "0.0.0",
         "@mdg-filius/fls": "0.0.0",
+        "@noble/hashes": "2.4.0",
         "yjs": "^13.6.33"
       }
     },