Merge: a log that survives the process, so the tablet can be debugged

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

# Conflicts:
#	apps/darkroom-android/Cargo.toml
#	apps/darkroom-desktop/Cargo.toml
#	platform/dr-plat/src/lib.rs

apps/darkroom-android/Cargo.toml

@@ -19,9 +19,10 @@ dr-ui.workspace = true
 # For `account::set_data_dir`: only the platform entry point knows where Android
 # lets this app keep files, and it must be set before any store is opened.
 dr-sync.workspace = true
-# For the panic hook, and for `crash::set_state_dir` — Android has no XDG
-# directories, so the entry point is the only place that knows where a crash
-# record may be written.
+# For the panic hook, for `state::set_state_dir` and for
+# `diagnostics::install`. Android has no XDG directories, so the entry point is
+# the only place that knows where a crash record or a log file may be written,
+# and both have to be in place before anything can fail.
 dr-plat.workspace = true
 # Directly, not just through dr-ui: `android_main` takes an `AndroidApp` and
 # calls `slint::android::init`, both of which come from this crate. The backend