Address #1386
The Shizuku branch of getPreferredInstaller() already fell back to the
session installer, but the guard hasShizukuPerm() called
Shizuku.checkSelfPermission(), which throws when the binder is not alive
(Shizuku disabled). The exception escaped before the fallback could run,
so installs failed instead of falling back.
- Guard hasShizukuPerm() on Shizuku.pingBinder() and swallow failures so
it returns false (instead of throwing) when Shizuku is unavailable,
letting the existing fallback run. This also fixes canInstallSilently().
- Detect when any chosen installer resolves to the default and optionally
inform the user via a toast, gated by notifyOnFallback so cancel/remove
callers stay silent while real install paths surface it.
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