fix(ios): restrict authentication capabilities and validate bootstrap types

Require iOS 18.4 for explicit upload denial in the isolated authentication window. Add origin-bound generated download policy, app-switcher privacy, typed metadata regressions and original community icon assets. Seven portable tests and Swift formatting checks pass; Apple SDK validation remains external.

scripts/generate-icon.py

@@ -0,0 +1,38 @@
+#!/usr/bin/env python3
+"""Generate the original community Y mark (not the upstream logo), without dependencies."""
+import json
+from pathlib import Path
+import struct
+import zlib
+
+ROOT = Path(__file__).resolve().parents[1]
+
+
+def png(size):
+    raw = bytearray()
+    segments = [(32, 29, 54, 54), (54, 54, 76, 29), (54, 54, 54, 80)]
+    for y in range(size):
+        raw.append(0)
+        for x in range(size):
+            coverage = 0
+            for dx, dy in [(0.25, 0.25), (0.75, 0.25), (0.25, 0.75), (0.75, 0.75)]:
+                px, py = (x + dx) * 108 / size, (y + dy) * 108 / size
+                for ax, ay, bx, by in segments:
+                    projection = max(0, min(1, ((px-ax)*(bx-ax)+(py-ay)*(by-ay))/((bx-ax)**2+(by-ay)**2)))
+                    if (px-ax-projection*(bx-ax))**2 + (py-ay-projection*(by-ay))**2 <= 4.5**2:
+                        coverage += 1
+                        break
+            raw.extend(round(background + (255-background)*coverage/4) for background in (108, 58, 237))
+
+    def chunk(name, data):
+        return struct.pack(">I", len(data)) + name + data + struct.pack(">I", zlib.crc32(name+data))
+    return b"\x89PNG\r\n\x1a\n" + chunk(b"IHDR", struct.pack(">IIBBBBB", size, size, 8, 2, 0, 0, 0)) + chunk(b"IDAT", zlib.compress(raw, 9)) + chunk(b"IEND", b"")
+
+
+if __name__ == "__main__":
+    folder = ROOT / "ios/Sources/Assets.xcassets/AppIcon.appiconset"
+    folder.mkdir(parents=True, exist_ok=True)
+    (folder / "AppIcon.png").write_bytes(png(1024))
+    (folder / "Contents.json").write_text(json.dumps({"images": [
+        {"filename": "AppIcon.png", "idiom": "universal", "platform": "ios", "size": "1024x1024"}
+    ], "info": {"author": "Yuvomi Mobile contributors", "version": 1}}, indent=2) + "\n")