Add an update script that re-applies changed patches

After a pull that changed a patch, prepare.py stopped: the patch neither
applied nor reverse-applied to a tree holding its earlier version. Now
it looks for the earlier version applied in that component -- the copy
it records in build/applied-patches, or a version from this
repository's history -- reverts exactly it and applies the new one.
It never resets a repository; when nothing matches it stops and names
the repository with other edits, and it restores the earlier version
if the new one does not apply.

scripts/update.sh runs build.sh, the base install and
install-runtime.sh, and refuses to start while a Riot Client or League
process is open, since the install steps stop Darling.

Checked on a sandbox Indium checkout holding the previous patch: the
result matches a clean apply, a second run is a no-op, an unrelated
local edit survives and a conflicting one stops with the error.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

docs/SETUP.md

@@ -28,6 +28,8 @@ The normal launcher starts neither an Electron inspector nor client API/UI helpe
 
 ## Updating an existing runtime
 
+`./scripts/update.sh` updates everything after `git pull`: `build.sh`, then the base install, then `install-runtime.sh`. When a pull changes a patch, `prepare.py` finds the earlier version applied in that component (its copy in `build/applied-patches`, or a version from this repository's history), reverts it, and applies the new one. It never resets a repository; if neither version matches, it stops and names the repository with other edits. The steps below update single components instead.
+
 These commands assume the pinned, patched source tree and its configured Makefiles already exist. From the repository root, build the two components with one worker to reduce resource contention:
 
 ```sh