Fix warnings, update deps, Metro-style task detail, comment counts

Warnings fixed:
- Removed unused imports (FieldMask, UpdateMemoRequest, LocalUriHandler,
  LocalPlatformContext, Composable in Color.kt)
- Removed unused Android color resources (old Material purple/teal)
- Replaced proguard-rules.pro with clean Compose/KMP config
- Fixed RelationDto to match actual API (memo/relatedMemo are objects)

Dependencies bumped:
- Ktor 3.4.3 → 3.5.0, Activity Compose 1.10.1 → 1.13.0
- Core KTX 1.16.0 → 1.18.0, SQLite 2.5.1 → 2.6.2
- WorkManager 2.11.1 → 2.11.2, JUnit 1.1.5 → 1.3.0, Espresso 3.5.1 → 3.7.0

Features:
- TaskDetailSheet converted to Metro AlertDialog style (no Material chips)
- MemoDetailScreen: edit button, created/updated timestamps at top
- Comment count shown on MemoCard header (computed from COMMENT relations)
- Explorer tag table: combined columns for memo count + task count per tag

Co-Authored-By: Claude Opus 4.6 (1M context)

Signed-off-by: Avinal Kumar <avinal.xlvii@gmail.com>

androidApp/proguard-rules.pro

@@ -5,11 +5,20 @@
 # kotlinx.serialization
 -keepattributes *Annotation*, InnerClasses
 -dontnote kotlinx.serialization.AnnotationsKt
--keepclassmembers class kotlinx.serialization.json.** { *** Companion; }
--keepclasseswithmembers class kotlinx.serialization.json.** { kotlinx.serialization.KSerializer serializer(...); }
--keep,includedescriptorclasses class com.avinal.memos.**$$serializer { *; }
--keepclassmembers class com.avinal.memos.** { *** Companion; }
--keepclasseswithmembers class com.avinal.memos.** { kotlinx.serialization.KSerializer serializer(...); }
+-keepclassmembers class kotlinx.serialization.json.** {
+    *** Companion;
+}
+-keepclasseswithmembers class kotlinx.serialization.json.** {
+    kotlinx.serialization.KSerializer serializer(...);
+}
+
+# Keep serializers generated for project model classes
+-keepclassmembers class com.avinal.memos.** {
+    *** Companion;
+}
+-keepclasseswithmembers class com.avinal.memos.** {
+    kotlinx.serialization.KSerializer serializer(...);
+}
 
 # Room
 -keep class * extends androidx.room.RoomDatabase

androidApp/src/main/res/values/colors.xml

@@ -1,10 +1,3 @@
 <?xml version="1.0" encoding="utf-8"?>
 <resources>
-    <color name="purple_200">#FFBB86FC</color>
-    <color name="purple_500">#FF6200EE</color>
-    <color name="purple_700">#FF3700B3</color>
-    <color name="teal_200">#FF03DAC5</color>
-    <color name="teal_700">#FF018786</color>
-    <color name="black">#FF000000</color>
-    <color name="white">#FFFFFFFF</color>
-</resources>
+</resources>