fix: use Build.DEVICE instead of Build.MODEL for hostname fallback

[TimeToBuildBob]

Problem

getDeviceName() in RustInterface.kt and SyncInterface.kt falls back to android.os.Build.MODEL when Settings.Global.DEVICE_NAME is null. Build.MODEL returns the OEM marketing name (e.g. "Poco F8 Ultra") which contains spaces — that breaks hostname-based bucket matching in aw-webui and aw-server.

Reported in #176: a Xiaomi Poco F8 Ultra produced "Poco F8 Ultra" as its hostname. The webui then fails to associate it with the Android bucket view because the hostname contains spaces.

Fix

Replace the Build.MODEL fallback with Build.DEVICE, which returns the device codename (poco_f8_ultra — lowercase, underscore-delimited, no spaces). This is the correct format for a network hostname.

Property	Example value	Hostname-safe?
Settings.Global.DEVICE_NAME	"Poco F8 Ultra"	❌ (spaces)
Build.MODEL	"Poco F8 Ultra"	❌ (spaces)
Build.DEVICE	"poco_f8_ultra"	✅

Changes

• RustInterface.kt: Build.MODEL → Build.DEVICE
• SyncInterface.kt: Build.MODEL → Build.DEVICE

Closes #176 (contributes — the hostname fix is one part of the broader stability tracker).

[greptile-apps]

Greptile Summary

This PR makes Android hostname fallback and normalization safer. The main changes are:

• Use Build.DEVICE instead of Build.MODEL when no configured device name is available.
• Ignore blank configured device names before falling back.
• Normalize hostnames to lowercase safe characters in both Rust and sync interfaces.

Confidence Score: 5/5

This looks safe to merge.

• No blocking issues found in the changed code.

Important Files Changed

Filename	Overview
mobile/src/main/java/net/activitywatch/android/RustInterface.kt	Updates local bucket hostname selection to skip blank names and apply strict normalization.
mobile/src/main/java/net/activitywatch/android/SyncInterface.kt	Applies the same normalized hostname selection before passing the value into sync calls.

_{Reviews (4): Last reviewed commit: "fix: filter blank DEVICE_NAME before fal..." | Re-trigger Greptile}

[TimeToBuildBob]

@greptileai review

[TimeToBuildBob]

@greptileai review

[TimeToBuildBob]

@greptileai review

[TimeToBuildBob]

CI-green and mergeable (Greptile 5/5) — waiting only on a maintainer click.

This PR is ready to merge, but the bot has pull-only access to this repo and can't self-merge — surfacing it here so it isn't lost. The monitoring loop will stop re-flagging it now that this note is posted.