feat(desktop): add Image Compression settings panel

Phase 3 of the desktop image compression plan.

ImageCompressionSettings composable in
desktopApp/.../ui/settings/, modeled on the existing
MediaServerSettings shape:

  - Section header "Image Compression"
  - Default quality as SingleChoiceSegmentedButtonRow (Low / Medium
    / Desktop High), matching the codebase convention from
    TorSettingsSection / FeedBuilderDialog (NOT a DropdownMenu).
  - Per-preset hint text underneath the segmented row, refreshed
    reactively as the user clicks.
  - Strip-metadata Switch with hint "Removes camera, GPS, and
    timestamp data from uploaded photos."

State flows from ImageCompressionStore via .collectAsState() — uses
the JVM-portable Compose API (collectAsStateWithLifecycle is
Android-only and is not used anywhere in desktopApp).

Integrated into Main.kt:1791 just below MediaServerSettings,
surrounded by the standard HorizontalDivider + Spacer rhythm.

Per-post override (compose dialog) will read from the same store
in Phase 4.

desktopApp/src/jvmMain/kotlin/com/vitorpamplona/amethyst/desktop/Main.kt

@@ -119,6 +119,7 @@ import com.vitorpamplona.amethyst.desktop.ui.media.LocalWindowState
 import com.vitorpamplona.amethyst.desktop.ui.profile.ProfileInfoCard
 import com.vitorpamplona.amethyst.desktop.ui.relay.LocalRelayCategories
 import com.vitorpamplona.amethyst.desktop.ui.relay.RelayStatusCard
+import com.vitorpamplona.amethyst.desktop.ui.settings.ImageCompressionSettings
 import com.vitorpamplona.amethyst.desktop.ui.settings.MediaServerSettings
 import com.vitorpamplona.amethyst.desktop.ui.settings.NamecoinSettingsSection
 import com.vitorpamplona.quartz.nip01Core.relay.client.reqs.SubscriptionListener
@@ -1787,6 +1788,12 @@ fun RelaySettingsScreen(
             HorizontalDivider()
             Spacer(Modifier.height(24.dp))
 
+            // Image Compression Settings
+            ImageCompressionSettings()
+            Spacer(Modifier.height(24.dp))
+            HorizontalDivider()
+            Spacer(Modifier.height(24.dp))
+
             // Tor Settings
             com.vitorpamplona.amethyst.desktop.ui.tor.TorSettingsSection(
                 torStatus = torStatus,

desktopApp/src/jvmMain/kotlin/com/vitorpamplona/amethyst/desktop/ui/settings/ImageCompressionSettings.kt

@@ -0,0 +1,123 @@
+/*
+ * Copyright (c) 2025 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.amethyst.desktop.ui.settings
+
+import androidx.compose.foundation.layout.Arrangement
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.Row
+import androidx.compose.foundation.layout.Spacer
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.height
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.SegmentedButton
+import androidx.compose.material3.SegmentedButtonDefaults
+import androidx.compose.material3.SingleChoiceSegmentedButtonRow
+import androidx.compose.material3.Switch
+import androidx.compose.material3.Text
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.collectAsState
+import androidx.compose.runtime.getValue
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.text.font.FontWeight
+import androidx.compose.ui.unit.dp
+import com.vitorpamplona.amethyst.commons.service.upload.CompressionQuality
+import com.vitorpamplona.amethyst.desktop.ImageCompressionStore
+
+/**
+ * Settings panel for image upload compression — quality preset +
+ * strip-EXIF toggle. Backed by [ImageCompressionStore]; changes
+ * persist to [com.vitorpamplona.amethyst.desktop.DesktopPreferences]
+ * immediately.
+ *
+ * Per-post overrides (in the compose dialog) read the current
+ * default from this store but do not write back.
+ */
+@Composable
+fun ImageCompressionSettings(modifier: Modifier = Modifier) {
+    val quality by ImageCompressionStore.quality.collectAsState()
+    val stripExif by ImageCompressionStore.stripExif.collectAsState()
+
+    Column(modifier = modifier.fillMaxWidth()) {
+        Text(
+            "Image Compression",
+            style = MaterialTheme.typography.titleMedium,
+            fontWeight = FontWeight.SemiBold,
+        )
+        Spacer(Modifier.height(12.dp))
+
+        Text(
+            "Default quality",
+            style = MaterialTheme.typography.bodyMedium,
+        )
+        Spacer(Modifier.height(8.dp))
+        SingleChoiceSegmentedButtonRow {
+            CompressionQuality.entries.forEachIndexed { index, preset ->
+                SegmentedButton(
+                    shape = SegmentedButtonDefaults.itemShape(index = index, count = CompressionQuality.entries.size),
+                    onClick = { ImageCompressionStore.setQuality(preset) },
+                    selected = preset == quality,
+                ) {
+                    Text(preset.displayName)
+                }
+            }
+        }
+        Spacer(Modifier.height(4.dp))
+        Text(
+            qualityHint(quality),
+            style = MaterialTheme.typography.bodySmall,
+            color = MaterialTheme.colorScheme.onSurfaceVariant,
+        )
+
+        Spacer(Modifier.height(20.dp))
+
+        Row(
+            modifier = Modifier.fillMaxWidth(),
+            horizontalArrangement = Arrangement.SpaceBetween,
+            verticalAlignment = Alignment.CenterVertically,
+        ) {
+            Column(modifier = Modifier.weight(1f)) {
+                Text(
+                    "Strip metadata before upload",
+                    style = MaterialTheme.typography.bodyMedium,
+                )
+                Spacer(Modifier.height(2.dp))
+                Text(
+                    "Removes camera, GPS, and timestamp data from uploaded photos.",
+                    style = MaterialTheme.typography.bodySmall,
+                    color = MaterialTheme.colorScheme.onSurfaceVariant,
+                )
+            }
+            Spacer(Modifier.height(0.dp))
+            Switch(
+                checked = stripExif,
+                onCheckedChange = ImageCompressionStore::setStripExif,
+            )
+        }
+    }
+}
+
+private fun qualityHint(quality: CompressionQuality): String =
+    when (quality) {
+        CompressionQuality.LOW -> "Smallest files — long edge max 640 px. Best for slow uplinks."
+        CompressionQuality.MEDIUM -> "Balanced — long edge max 640 px, moderate quality."
+        CompressionQuality.DESKTOP_HIGH -> "Good quality for desktop — long edge max 1920 px."
+    }