feat: check for updates page in settings

Add a full-screen update checker accessible from a button at the
bottom of the settings page. It queries the fork's GitHub latest
release and can download + install the APK in place.

- UpdateRepository (core/data): fetch releases/latest via GitHub API,
  parse tag/description/APK asset, stream APK download to cacheDir
- VersionComparator (core/domain): compare 4.4.6-ba7opf.N style tags
  (base version first, then build number; v-prefix tolerant) + tests
- IMainContainer/MainContainer: inject updateRepo
- UpdateCheckerScreen (feature/settings): shows current version,
  checks for updates, displays latest version + release notes, and a
  Download & install button; FileProvider hands the APK to the
  system installer
- SettingsScreen: bottom entry button, full-screen page toggle
- AndroidManifest: REQUEST_INSTALL_PACKAGES permission + FileProvider
- i18n strings (en/zh)

core/domain/src/main/java/com/rtbishop/look4sat/core/domain/model/LatestRelease.kt

@@ -0,0 +1,9 @@
+package com.rtbishop.look4sat.core.domain.model
+
+/** Latest release info fetched from the fork's GitHub releases API. */
+data class LatestRelease(
+    val versionTag: String, // e.g. "v4.4.6-ba7opf.6"
+    val title: String,      // release name, may be empty
+    val body: String,       // release notes / update description
+    val apkUrl: String?     // first .apk asset download URL, null if absent
+)

core/domain/src/main/java/com/rtbishop/look4sat/core/domain/repository/IMainContainer.kt

@@ -31,6 +31,7 @@ interface IMainContainer {
     val satelliteRepo: ISatelliteRepo
     val databaseRepo: IDatabaseRepo
     val amSatRepo: IAmSatRepository
+    val updateRepo: IUpdateRepository
     val radioTrackingService: IRadioTrackingService
     val mutualPassData: StateFlow<MutualPassData>
     fun setMutualPassData(data: MutualPassData)

core/domain/src/main/java/com/rtbishop/look4sat/core/domain/repository/IUpdateRepository.kt

@@ -0,0 +1,12 @@
+package com.rtbishop.look4sat.core.domain.repository
+
+import com.rtbishop.look4sat.core.domain.model.LatestRelease
+import java.io.File
+
+interface IUpdateRepository {
+    /** Fetch the latest release of the fork repo from GitHub; null on failure. */
+    suspend fun getLatestRelease(): LatestRelease?
+
+    /** Download the release APK from [url] into [dest]; true on success. */
+    suspend fun downloadApk(url: String, dest: File): Boolean
+}

core/domain/src/main/java/com/rtbishop/look4sat/core/domain/utility/VersionComparator.kt

@@ -0,0 +1,44 @@
+package com.rtbishop.look4sat.core.domain.utility
+
+/**
+ * Compares two version strings of the form "<major>.<minor>.<patch>[-<build>]" used by the
+ * BA7OPF fork releases (e.g. "4.4.6-ba7opf.6" or "v4.4.6-ba7opf.7").
+ *
+ * The comparison is done on the numeric version segments first; when the base versions are
+ * equal, the trailing build number (if any) decides. This lets a "4.4.6-ba7opf.7" release be
+ * detected as newer than "4.4.6-ba7opf.6" while "4.5.0" trumps any "4.4.x" build.
+ */
+object VersionComparator {
+
+    /** True when [candidate] is a newer version than [current]. */
+    fun isNewer(candidate: String, current: String): Boolean {
+        val cand = parse(candidate)
+        val curr = parse(current)
+        val maxLen = maxOf(cand.first.size, curr.first.size)
+        for (i in 0 until maxLen) {
+            val c = cand.first.getOrElse(i) { 0 }
+            val k = curr.first.getOrElse(i) { 0 }
+            if (c != k) return c > k
+        }
+        return cand.second > curr.second
+    }
+
+    /**
+     * Parses a version string into (numeric base segments, trailing build number).
+     * "v4.4.6-ba7opf.7" -> ([4,4,6], 7); "4.4.6" -> ([4,4,6], 0); "4.4.6-ba7opf" -> ([4,4,6], 0).
+     */
+    fun parse(version: String): Pair<List<Int>, Int> {
+        val cleaned = version.trim().removePrefix("v")
+        val dashIndex = cleaned.indexOf('-')
+        val basePart = if (dashIndex >= 0) cleaned.substring(0, dashIndex) else cleaned
+        val suffixPart = if (dashIndex >= 0) cleaned.substring(dashIndex + 1) else ""
+        val base = basePart.split('.').mapNotNull { it.toIntOrNull() }
+        // The build number is the trailing numeric segment of the suffix (e.g. "ba7opf.7" -> 7).
+        val build = suffixPart
+            .split('.')
+            .lastOrNull()
+            ?.toIntOrNull()
+            ?: 0
+        return base to build
+    }
+}

core/domain/src/test/java/com/rtbishop/look4sat/core/domain/VersionComparatorTest.kt

@@ -0,0 +1,48 @@
+package com.rtbishop.look4sat.core.domain
+
+import com.rtbishop.look4sat.core.domain.utility.VersionComparator
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertFalse
+import org.junit.Assert.assertTrue
+import org.junit.Test
+
+class VersionComparatorTest {
+
+    @Test
+    fun `newer build number wins when base version equal`() {
+        assertTrue(VersionComparator.isNewer("4.4.6-ba7opf.7", "4.4.6-ba7opf.6"))
+        assertTrue(VersionComparator.isNewer("v4.4.6-ba7opf.6", "4.4.6-ba7opf.5"))
+    }
+
+    @Test
+    fun `newer base version wins regardless of build number`() {
+        assertTrue(VersionComparator.isNewer("4.5.0", "4.4.6-ba7opf.99"))
+        assertTrue(VersionComparator.isNewer("4.4.7-ba7opf.1", "4.4.6-ba7opf.99"))
+    }
+
+    @Test
+    fun `older versions are not newer`() {
+        assertFalse(VersionComparator.isNewer("4.4.6-ba7opf.5", "4.4.6-ba7opf.6"))
+        assertFalse(VersionComparator.isNewer("4.4.5", "4.4.6-ba7opf.1"))
+        assertFalse(VersionComparator.isNewer("4.4.6-ba7opf.6", "4.4.6-ba7opf.6"))
+    }
+
+    @Test
+    fun `v prefix is ignored`() {
+        assertTrue(VersionComparator.isNewer("v4.4.7", "4.4.6"))
+        assertFalse(VersionComparator.isNewer("v4.4.6", "4.4.6-ba7opf.1"))
+    }
+
+    @Test
+    fun `non numeric suffix without number treated as zero build`() {
+        assertTrue(VersionComparator.isNewer("4.4.6-ba7opf.1", "4.4.6-ba7opf"))
+        assertFalse(VersionComparator.isNewer("4.4.6-ba7opf", "4.4.6-ba7opf.1"))
+    }
+
+    @Test
+    fun `parse extracts base and build number`() {
+        assertEquals(listOf(4, 4, 6) to 7, VersionComparator.parse("v4.4.6-ba7opf.7"))
+        assertEquals(listOf(4, 4, 6) to 0, VersionComparator.parse("4.4.6"))
+        assertEquals(listOf(4, 4, 6) to 0, VersionComparator.parse("4.4.6-ba7opf"))
+    }
+}