Fetch pinned darling-swift LFS objects from GitHub, not the dead host

The pinned src/external/swift/.lfsconfig points lfs.url at the retired
git-lfs.darlinghq.org, so a fresh `git submodule update --init --recursive`
blocks with no output right after src/external/sqlite is checked out: swift is
the next submodule in sorted order and its checkout waits on that host.

Override lfs.url to GitHub's endpoint, which still serves the objects (verified
44 objects / 16 MB, real Mach-O dylibs), and print explicit submodule progress so
the last completed submodule is not mistaken for the stalled one.

docs/SETUP.md

@@ -2,7 +2,7 @@
 
 The patch manifest pins Darling to `60ba801decee7a00782f74f6be4c8ffb013f79ff` and records every changed submodule's revision. `scripts/prepare.py` checks each revision before applying patches and never resets an existing checkout to make a patch apply. Re-running it accepts an already-applied patch.
 
-Git LFS must be available before fetching the upstream submodules. The local development checkout had removed prebuilt Swift files from its working directory; that deletion is deliberately not exported. A fresh upstream checkout keeps its original Swift assets and licensing. Do not install Git LFS pointer text as a library.
+Git LFS must be available before fetching the upstream submodules. The pinned `darling-swift` submodule's `.lfsconfig` points at the retired `git-lfs.darlinghq.org`, which no longer accepts connections; `prepare.py` redirects that submodule's LFS requests to GitHub, which still serves the objects. Without that override a fresh `git submodule update` blocks with no output right after `src/external/sqlite` is checked out. The local development checkout had removed prebuilt Swift files from its working directory; that deletion is deliberately not exported. A fresh upstream checkout keeps its original Swift assets and licensing. Do not install Git LFS pointer text as a library.
 
 `configure.py` renders `@PROJECT_ROOT@`, `@HOST_HOME@`, `@GUEST_HOME@`, `@GUEST_USER@`, `@DPREFIX@` and `@DARLING_SDK@` into ignored local copies. A build-directory symlink preserves the original scripts' relative build layout. The public source files remain machine-independent.
 

docs/TROUBLESHOOTING.md

@@ -75,6 +75,7 @@ A separate multi-window path stopped the active async presenter when another dif
 - **Build process killed:** lower parallelism, for example `JOBS=2 ./scripts/build.sh` or `--parallel 1` for an incremental component build.
 - **Incremental helper cannot find `flags.make` or `link.txt`:** use Unix Makefiles, not Ninja.
 - **Prebuilt Swift file contains Git LFS pointer text:** install Git LFS and fetch the original upstream assets; pointer text is not a usable library.
+- **Submodule fetch stops with no output right after `src/external/sqlite`:** the next submodule is `src/external/swift`, whose pinned `.lfsconfig` points at the retired `git-lfs.darlinghq.org`. The checkout is blocked on that host, not on sqlite. `prepare.py` redirects that submodule's LFS requests to GitHub. To finish a fetch that was interrupted before any patches were applied, run `git -C build/darling-src -c lfs.url=https://github.com/darlinghq/darling-swift.git/info/lfs submodule update --init --recursive --progress`, then re-run `./scripts/build.sh`. Do not run that submodule update once `prepare.py` has applied patches: it resets every submodule working tree to the pinned revision and discards the patches.
 
 ## Lower fight FPS than Windows
 

scripts/prepare.py

@@ -13,7 +13,16 @@ if not (source/'.git').exists():
     source.parent.mkdir(parents=True,exist_ok=True)
     run(['git','clone',manifest['upstream'],str(source)])
     run(['git','-C',str(source),'checkout','--detach',manifest['revision']])
-    run(['git','-C',str(source),'submodule','update','--init','--recursive'])
+    # Recursive initialization can spend a long time fetching nested repos (and
+    # Git LFS assets). Explicit progress keeps the last completed submodule
+    # from looking like the operation that is currently stuck. The pinned
+    # darling-swift .lfsconfig points at the retired git-lfs.darlinghq.org, so
+    # fetch that submodule's LFS objects from GitHub, which still serves them;
+    # otherwise the checkout blocks on the dead host right after sqlite.
+    print('Initializing Darling submodules (large repositories/LFS assets may take a while)...',flush=True)
+    run(['git','-C',str(source),'-c','lfs.url=https://github.com/darlinghq/darling-swift.git/info/lfs',
+         'submodule','update','--init','--recursive','--progress'])
+    print('Darling submodules initialized.',flush=True)
 # Never reset someone else's checkout to make a patch apply.
 for component in manifest['components']:
     repo=source/component['path']