Set up Android project with Kotlin and Jetpack Compose

Initial project structure with manifest configured for foreground
audio service, AudioTrack-based playback, and background operation.
Includes Gradle wrapper, dependency catalog, placeholder icons,
and build instructions for Arch Linux.

AGENTS.md

@@ -0,0 +1,94 @@
+# AGENTS.md — Agent Working Guide for Pacer
+
+## Purpose
+This file explains how AI agents should work with the Pacer project. Follow these rules
+consistently across sessions, as different agents may work on different themes or user stories.
+
+## Agent Environment
+- Runs inside a Docker container with `sudo` rights
+- Install any required tools via `sudo pacman -S <package>` or `paru -S <package>` (AUR)
+- No need to ask the user to install dependencies — just install them as needed
+
+## Project Structure
+
+```
+Pacer/
+├── AGENTS.md                 ← this file
+├── BACKLOG.md                ← all user stories and acceptance criteria
+├── README.md                 ← build instructions for humans
+├── gradlew                   ← always use this to build, never system gradle
+├── gradle/
+│   ├── libs.versions.toml    ← single source of truth for all dependency versions
+│   └── wrapper/
+├── settings.gradle.kts
+├── build.gradle.kts          ← root build file (apply false only)
+└── app/
+    ├── build.gradle.kts      ← module build file
+    └── src/
+        ├── main/
+        │   ├── AndroidManifest.xml
+        │   ├── kotlin/net/jeena/pacer/   ← all Kotlin source files
+        │   └── res/
+        ├── test/kotlin/net/jeena/pacer/          ← unit tests
+        └── androidTest/kotlin/net/jeena/pacer/   ← instrumented tests
+```
+
+## Package Name
+All Kotlin source files use the package prefix `net.jeena.pacer`.
+
+## Naming Conventions
+- Activities: `*Activity.kt` (e.g., `MainActivity.kt`)
+- Services: `*Service.kt` (e.g., `PacerService.kt`)
+- Composables: `*Screen.kt` for full screens, `*Component.kt` for reusable UI
+- ViewModels: `*ViewModel.kt`
+
+## Code Rules (Never Violate)
+- Kotlin only — no Java files
+- All UI via Jetpack Compose — no XML layouts
+- **No audio focus requests anywhere** — app must play alongside AntennaPod without interruption
+- Use `AudioTrack` directly for audio — not `MediaPlayer` or `ExoPlayer`
+- `minSdk = 24` — use version checks for APIs above this
+- Single-activity architecture — do not add new Activities for new screens
+- All dependency versions in `gradle/libs.versions.toml` — never hardcode versions
+
+## How to Use the BACKLOG
+
+Stories are identified as `US-XX` in BACKLOG.md, grouped by Theme.
+
+### Workflow Per User Story
+1. Read the acceptance criteria for the target story in BACKLOG.md.
+2. For TDD stories (US-03, US-04, US-13, US-14): write the failing test first.
+3. Implement the minimum code to satisfy acceptance criteria.
+4. Verify: `./gradlew lint` passes, `./gradlew test` passes.
+
+### TDD Stories
+For US-03, US-04, US-13:
+- Commit failing test first: `test(US-XX): add failing test for <feature>`
+- Then implement and commit: `feat(US-XX): implement <feature>`
+
+### Commit Message Convention
+```
+<type>(US-XX): <short description>
+
+Types: feat, fix, test, refactor, docs, chore
+Example: feat(US-03): generate 880 Hz sine wave with AudioTrack
+```
+
+## Build Commands
+
+```bash
+./gradlew assembleDebug        # build debug APK
+./gradlew test                 # run unit tests
+./gradlew connectedAndroidTest # run instrumented tests (requires device)
+./gradlew lint                 # run lint checks
+./gradlew installDebug         # install on connected device
+./gradlew clean assembleDebug  # clean build
+```
+
+Output APK: `app/build/outputs/apk/debug/app-debug.apk`
+
+## Key Architecture Notes
+- Background audio uses `HandlerThread` for the scheduling loop (battery-efficient)
+- `WAKE_LOCK` + foreground service keeps audio alive through Doze mode
+- `foregroundServiceType="mediaPlayback"` is required on Android 14+ (already in manifest)
+- Do not add new dependencies without a user story requiring them