feat(US-06): use JetBrains Mono font and rectangular buttons

Bundle JetBrains Mono Regular and Bold TTF files for a modern
monospace look without needing network access. All buttons now
use RectangleShape to match the sharp-cornered style of the
original web version.

app/src/main/kotlin/net/jeena/pacer/ui/PacerScreen.kt

@@ -34,6 +34,7 @@ import androidx.compose.ui.geometry.Size
 import androidx.compose.ui.graphics.Color
 import androidx.compose.ui.graphics.drawscope.Stroke
 import androidx.compose.ui.graphics.lerp
+import androidx.compose.ui.graphics.RectangleShape
 import androidx.compose.ui.text.font.FontFamily
 import androidx.compose.ui.text.font.FontWeight
 import androidx.compose.ui.unit.dp
@@ -42,6 +43,7 @@ import kotlinx.coroutines.launch
 import net.jeena.pacer.BpmCalculator
 import net.jeena.pacer.PacerService
 import net.jeena.pacer.PacerViewModel
+import net.jeena.pacer.ui.theme.JetBrainsMono
 
 private val BG     = Color(0xFF0A0A0A)
 private val FG     = Color(0xFFF0EDE8)
@@ -119,7 +121,7 @@ fun PacerScreen(viewModel: PacerViewModel, modifier: Modifier = Modifier) {
             Text(
                 text = "PACER",
                 fontSize = 13.sp,
-                fontFamily = FontFamily.Monospace,
+                fontFamily = JetBrainsMono,
                 color = FG.copy(alpha = 0.4f),
                 letterSpacing = 5.sp
             )
@@ -130,14 +132,14 @@ fun PacerScreen(viewModel: PacerViewModel, modifier: Modifier = Modifier) {
                     text = "$bpm",
                     fontSize = 80.sp,
                     fontWeight = FontWeight.Bold,
-                    fontFamily = FontFamily.Monospace,
+                    fontFamily = JetBrainsMono,
                     color = bpmColor,
                     letterSpacing = (-2).sp
                 )
                 Text(
                     text = "BPM",
                     fontSize = 11.sp,
-                    fontFamily = FontFamily.Monospace,
+                    fontFamily = JetBrainsMono,
                     color = FG.copy(alpha = 0.35f),
                     letterSpacing = 4.sp
                 )
@@ -168,6 +170,7 @@ fun PacerScreen(viewModel: PacerViewModel, modifier: Modifier = Modifier) {
             // Start/Stop button
             OutlinedButton(
                 onClick = { viewModel.togglePlayback() },
+                shape = RectangleShape,
                 border = BorderStroke(2.dp, if (isPlaying) ACCENT else FG),
                 colors = ButtonDefaults.outlinedButtonColors(
                     contentColor = if (isPlaying) BG else FG,
@@ -178,7 +181,7 @@ fun PacerScreen(viewModel: PacerViewModel, modifier: Modifier = Modifier) {
                     text = if (isPlaying) "STOP" else "START",
                     fontSize = 18.sp,
                     fontWeight = FontWeight.Bold,
-                    fontFamily = FontFamily.Monospace,
+                    fontFamily = JetBrainsMono,
                     letterSpacing = 3.sp,
                     modifier = Modifier.padding(horizontal = 16.dp, vertical = 4.dp)
                 )
@@ -189,7 +192,7 @@ fun PacerScreen(viewModel: PacerViewModel, modifier: Modifier = Modifier) {
                 Text(
                     text = "PACE",
                     fontSize = 10.sp,
-                    fontFamily = FontFamily.Monospace,
+                    fontFamily = JetBrainsMono,
                     color = FG.copy(alpha = 0.35f),
                     letterSpacing = 3.sp
                 )
@@ -212,6 +215,7 @@ fun PacerScreen(viewModel: PacerViewModel, modifier: Modifier = Modifier) {
                         OutlinedButton(
                             onClick = { viewModel.updateBpm(preset) },
                             modifier = Modifier.size(width = 72.dp, height = 48.dp),
+                            shape = RectangleShape,
                             contentPadding = PaddingValues(0.dp),
                             border = BorderStroke(1.dp, if (active) ACCENT else DIM),
                             colors = ButtonDefaults.outlinedButtonColors(
@@ -224,12 +228,12 @@ fun PacerScreen(viewModel: PacerViewModel, modifier: Modifier = Modifier) {
                                     text = "$preset",
                                     fontSize = 13.sp,
                                     fontWeight = FontWeight.Bold,
-                                    fontFamily = FontFamily.Monospace
+                                    fontFamily = JetBrainsMono
                                 )
                                 Text(
                                     text = label,
                                     fontSize = 9.sp,
-                                    fontFamily = FontFamily.Monospace,
+                                    fontFamily = JetBrainsMono,
                                     letterSpacing = 1.sp
                                 )
                             }
@@ -243,7 +247,7 @@ fun PacerScreen(viewModel: PacerViewModel, modifier: Modifier = Modifier) {
                 Text(
                     text = "VOLUME  ${(volume * 100).toInt()}%",
                     fontSize = 10.sp,
-                    fontFamily = FontFamily.Monospace,
+                    fontFamily = JetBrainsMono,
                     color = FG.copy(alpha = 0.35f),
                     letterSpacing = 3.sp
                 )

app/src/main/kotlin/net/jeena/pacer/ui/theme/Font.kt

@@ -0,0 +1,11 @@
+package net.jeena.pacer.ui.theme
+
+import androidx.compose.ui.text.font.Font
+import androidx.compose.ui.text.font.FontFamily
+import androidx.compose.ui.text.font.FontWeight
+import net.jeena.pacer.R
+
+val JetBrainsMono = FontFamily(
+    Font(R.font.jetbrainsmono_regular, FontWeight.Normal),
+    Font(R.font.jetbrainsmono_bold, FontWeight.Bold),
+)