refactor(privacy): drop I2pType.INTERNAL — EXTERNAL is the permanent answer

Earlier commits kept I2pType.INTERNAL as a placeholder for a follow-up
embedded daemon. We're not shipping that: I2P bootstrap on Android is
structurally minutes-long (no equivalent of Tor's hardcoded directory
authorities — NetDB peer discovery is protocol-inherent), so an embedded
router would mean a permanently-warming UX. Users who want I2P run i2pd /
Java I2P independently and point Amethyst at its SOCKS port.

Changes:
- commons I2pType drops the INTERNAL variant; parseI2pType collapses unknown
  codes to OFF
- I2pManager loses its INTERNAL switch arm
- I2pSettingsDialog drops the "treat INTERNAL as OFF" mapping it used to
  carry — the enum no longer has the case
- Android UI I2pSettings.resourceId drops the i2p_internal branch
- strings.xml drops the now-unused i2p_internal string
- I2pSharedPreferences hardens load: a stored "INTERNAL" from an earlier
  branch is no longer a valid I2pType, so runCatching swallows the
  IllegalArgumentException and the user lands on OFF
- PrivacyRouterTest fixtures use I2pType.EXTERNAL throughout

commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/i2p/I2pSettings.kt

@@ -41,17 +41,20 @@ data class I2pSettings(
     val mediaUploadsViaI2p: Boolean = false,
 )
 
+// EXTERNAL-only: this app does not embed an I2P router. Bootstrap on Android is
+// minutes-long for a fresh netDb and the protocol provides no shortcut analogous
+// to Tor's hardcoded directory authorities; we'd ship a "permanently warming up"
+// experience. Users who want I2P run i2pd or Java I2P independently and point
+// Amethyst at its SOCKS port (default 4447). See I2pManager.
 enum class I2pType(
     val screenCode: Int,
 ) {
     OFF(0),
-    INTERNAL(1),
     EXTERNAL(2),
 }
 
 fun parseI2pType(code: Int?): I2pType =
     when (code) {
-        I2pType.INTERNAL.screenCode -> I2pType.INTERNAL
         I2pType.EXTERNAL.screenCode -> I2pType.EXTERNAL
         else -> I2pType.OFF
     }

commons/src/commonTest/kotlin/com/vitorpamplona/amethyst/commons/privacy/PrivacyRouterTest.kt

@@ -38,7 +38,7 @@ class PrivacyRouterTest {
         i2pOn: Boolean = false,
         preferred: PrivacyTransport = PrivacyTransport.DIRECT,
         tor: TorSettings = TorSettings(torType = if (torOn) TorType.INTERNAL else TorType.OFF),
-        i2p: I2pSettings = I2pSettings(i2pType = if (i2pOn) I2pType.INTERNAL else I2pType.OFF),
+        i2p: I2pSettings = I2pSettings(i2pType = if (i2pOn) I2pType.EXTERNAL else I2pType.OFF),
     ) = PrivacySettings(
         tor = tor,
         i2p = i2p,
@@ -125,7 +125,7 @@ class PrivacyRouterTest {
             settings(
                 i2pOn = true,
                 preferred = PrivacyTransport.I2P,
-                i2p = I2pSettings(i2pType = I2pType.INTERNAL, videosViaI2p = true),
+                i2p = I2pSettings(i2pType = I2pType.EXTERNAL, videosViaI2p = true),
             )
         assertEquals(PrivacyRoute.I2p, PrivacyRouter.route(clearnet, FeatureRole.VIDEO, s))
     }
@@ -136,7 +136,7 @@ class PrivacyRouterTest {
             settings(
                 i2pOn = true,
                 preferred = PrivacyTransport.I2P,
-                i2p = I2pSettings(i2pType = I2pType.INTERNAL, videosViaI2p = false),
+                i2p = I2pSettings(i2pType = I2pType.EXTERNAL, videosViaI2p = false),
             )
         assertEquals(PrivacyRoute.Direct, PrivacyRouter.route(clearnet, FeatureRole.VIDEO, s))
     }
@@ -162,7 +162,7 @@ class PrivacyRouterTest {
                 torOn = false,
                 i2pOn = true,
                 preferred = PrivacyTransport.TOR,
-                i2p = I2pSettings(i2pType = I2pType.INTERNAL, imagesViaI2p = true),
+                i2p = I2pSettings(i2pType = I2pType.EXTERNAL, imagesViaI2p = true),
             )
         assertEquals(PrivacyRoute.Direct, PrivacyRouter.route(clearnet, FeatureRole.IMAGE, s))
     }
@@ -176,7 +176,7 @@ class PrivacyRouterTest {
                 i2pOn = true,
                 preferred = PrivacyTransport.I2P,
                 tor = TorSettings(torType = TorType.INTERNAL, imagesViaTor = true),
-                i2p = I2pSettings(i2pType = I2pType.INTERNAL, imagesViaI2p = true),
+                i2p = I2pSettings(i2pType = I2pType.EXTERNAL, imagesViaI2p = true),
             )
         assertEquals(PrivacyRoute.I2p, PrivacyRouter.route(clearnet, FeatureRole.IMAGE, s))
     }