feat: add Downloads section for offline playback in Android Auto

[sinful1992]

What

Adds a Downloads section to the Android Auto browse tree, served entirely from the local Room download table - zero network calls - so downloaded music is browsable and playable in the car even with no connectivity at all.

• New [downloadedID] node, placed as the first child of Home/More (it is the only section that works with no connectivity).
• AutomotiveRepository.getDownloadedSongs() reads DownloadDao.getAllSync() on a background thread and maps through the existing MappingUtil.mapMediaItems(..., QUEUE_CACHED_SOURCE) path - the same mapping the rest of AA uses. MappingUtil.getUri() already resolves downloaded songs to their local file, so items play fully offline.
• Queue behavior on tap matches Starred tracks (cached-source queue resolution).
• Reuses the existing translated download_title_section string; adds one AA icon drawable.

Why

MediaBrowserTree previously built every section from server requests, so in a dead zone or tunnel Android Auto showed nothing playable even with gigabytes of downloaded music on the phone. Driving is exactly where connectivity is least reliable. Related pain points: #810, #811. Refs #860.

Testing

• Built assembleTempusDebug locally.
• Tempus flavor only (the degoogled flavor has no AA browse tree).

Summary by CodeRabbit

• New Features
  • Added a Downloaded section to the Android Auto media browsing experience.
  • Downloaded content is now shown directly in the hierarchy (with results limited to the app’s supported maximum).
  • Included a dedicated Downloaded icon for clearer navigation.

[coderabbitai]

📝 Walkthrough

Walkthrough

Adds a downloaded songs section to the Android Auto media hierarchy, backed by locally stored downloads and rendered with a new identifier and icon.

Changes

Downloaded songs in Android Auto

Layer / File(s)	Summary
Downloaded song retrieval app/src/tempus/java/com/cappielloantonio/tempo/repository/AutomotiveRepository.java	Adds getDownloadedSongs(), which asynchronously reads downloaded records, limits the result, maps them to MediaItem instances, and returns a LibraryResult.
Android Auto downloaded section app/src/tempus/java/com/cappielloantonio/tempo/service/MediaBrowserTree.kt, app/src/tempus/java/com/cappielloantonio/tempo/util/ConstantsAA.kt, app/src/tempus/res/drawable/ic_aa_downloaded.xml	Registers the downloaded section under the Android Auto home node, routes child requests to the repository, and adds its identifier and artwork.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Sequence Diagram(s)

sequenceDiagram
  participant AndroidAuto
  participant MediaBrowserTree
  participant AutomotiveRepository
  participant downloadDao
  AndroidAuto->>MediaBrowserTree: Request downloaded section
  MediaBrowserTree->>AutomotiveRepository: getDownloadedSongs()
  AutomotiveRepository->>downloadDao: getAllSync()
  downloadDao-->>AutomotiveRepository: Download records
  AutomotiveRepository-->>MediaBrowserTree: LibraryResult with MediaItems
  MediaBrowserTree-->>AndroidAuto: Downloaded songs

Loading

Possibly related issues

• [Feature Request] - Android Auto: Downloads section for offline playback #860 — Requests the Android Auto Downloads section backed by locally downloaded songs.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the main change: adding a Downloads section for offline playback in Android Auto.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands.}

[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In
`@app/src/tempus/java/com/cappielloantonio/tempo/repository/AutomotiveRepository.java`:
- Around line 375-391: Wrap the background thread body in the
AutomotiveRepository flow that loads downloads and builds mediaItems in a
try-catch, including getAllSync, setChildrenMetadata, and
MappingUtil.mapMediaItems. On any exception, always resolve listenableFuture
with the appropriate error result instead of leaving it pending; preserve the
existing successful and empty-list results.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 478c993f-735d-43dc-b761-31b49ae0f665

📥 Commits

Reviewing files that changed from the base of the PR and between 3fe7074 and 62a6876.

📒 Files selected for processing (4)

• app/src/tempus/java/com/cappielloantonio/tempo/repository/AutomotiveRepository.java
• app/src/tempus/java/com/cappielloantonio/tempo/service/MediaBrowserTree.kt
• app/src/tempus/java/com/cappielloantonio/tempo/util/ConstantsAA.kt
• app/src/tempus/res/drawable/ic_aa_downloaded.xml