Keep mise upgrades from pruning versions still in use

mise ships with upgrade.auto_prune on, so `mise up` deletes the old
install directory as soon as a tool upgrades. Long-running processes are
still executing out of that directory, and some re-exec themselves by
absolute path, so running `omarchy update` or `mup` breaks them mid-session.

Claude Code is the case that surfaced it. It records its own binary path
at startup and dispatches its bundled ugrep and bfs through it, so once
the upgrade pruned that path its grep and find wrappers fell back to the
mise wrapper in ~/.local/bin. That wrapper cannot stand in for the real
binary here: a shebang script never sees the argv[0] it was invoked
under, because the kernel hands the interpreter the script path instead.
The dispatch collapsed to plain `claude -G`, which fails.

Keeping the old versions costs some disk and leaves the stale directory
behind until something prunes it deliberately, which is the cheaper half
of the trade.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

install/user/mise.sh

@@ -1,3 +1,7 @@
+# Upgrades must not delete the version a running process is executing from:
+# mise up would prune the old install dir out from under a live session.
+mise settings set upgrade.auto_prune false
+
 omarchy-mise-install codex
 omarchy-mise-install claude
 omarchy-mise-install crush

migrations/1787215483.sh

@@ -0,0 +1,3 @@
+echo "Stop mise upgrades from pruning versions still in use"
+
+mise settings set upgrade.auto_prune false