refactor: move feature-not-yet-iOS-ready files to jvmAndroid

Clears the remaining easy iOS blockers in commons/commonMain by
relocating files whose underlying feature isn't iOS-ready yet, rather
than fabricating expect/actuals we won't need until that feature ships.

- NestViewModel + ActiveSubscription: depend on :nestsClient (audio
  rooms — Phase 5 per the iOS plan). Moved as-is; both already lived
  in a jvmAndroid-shaped package.
- HtmlCharsetParser: depends on java.nio.charset.Charset, used only
  by the Android link-preview pipeline (no Desktop / iOS consumer
  today).
- RenderMarkdown: depends on com.halilibo.richtext.* — needs iOS
  artifact verification before it can return to commonMain (tracked
  for Phase 3).
- MediaContentModels.kt is split:
  * URL-based models (BaseMediaContent, MediaUrlImage/Video/Pdf,
    EncryptedMediaUrlImage/Video) stay in commonMain — pure KMP, no
    java.io.File reference.
  * Locally-cached variants (MediaPreloadedContent, MediaLocalImage,
    MediaLocalVideo) move to a new MediaLocalContent.kt under
    jvmAndroid — they hold a java.io.File and call .exists().

After this PR commons/commonMain has 5 remaining java.* importers
(Note's BigDecimal, the two SortedSet observables, URL parsing in
RichTextParser + UrlInfoItem). Down from 18 at the start of Phase 2.

commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/richtext/MediaContentModels.kt

@@ -22,7 +22,11 @@ package com.vitorpamplona.amethyst.commons.richtext
 
 import androidx.compose.runtime.Immutable
 import com.vitorpamplona.quartz.nip94FileMetadata.tags.DimensionTag
-import java.io.File
+
+// URL-based media content models (KMP). The locally-cached variants
+// (MediaPreloadedContent, MediaLocalImage, MediaLocalVideo) live in
+// MediaLocalContent.kt under the jvmAndroid source set because they depend
+// on java.io.File.
 
 @Immutable
 abstract class BaseMediaContent(
@@ -123,44 +127,3 @@ class EncryptedMediaUrlVideo(
     thumbhash: String? = null,
     authorPubKey: String? = null,
 ) : MediaUrlVideo(url, description, hash, dim, uri, artworkUri, authorName, blurhash, contentWarning, mimeType, thumbhash, authorPubKey = authorPubKey)
-
-@Immutable
-abstract class MediaPreloadedContent(
-    val localFile: File?,
-    description: String? = null,
-    val mimeType: String? = null,
-    val isVerified: Boolean? = null,
-    dim: DimensionTag? = null,
-    blurhash: String? = null,
-    val uri: String,
-    val id: String? = null,
-    thumbhash: String? = null,
-) : BaseMediaContent(description, dim, blurhash, thumbhash) {
-    fun localFileExists() = localFile != null && localFile.exists()
-}
-
-@Immutable
-class MediaLocalImage(
-    localFile: File?,
-    mimeType: String? = null,
-    description: String? = null,
-    dim: DimensionTag? = null,
-    blurhash: String? = null,
-    isVerified: Boolean? = null,
-    uri: String,
-    thumbhash: String? = null,
-) : MediaPreloadedContent(localFile, description, mimeType, isVerified, dim, blurhash, uri, thumbhash = thumbhash)
-
-@Immutable
-class MediaLocalVideo(
-    localFile: File?,
-    mimeType: String? = null,
-    description: String? = null,
-    dim: DimensionTag? = null,
-    blurhash: String? = null,
-    isVerified: Boolean? = null,
-    uri: String,
-    val artworkUri: String? = null,
-    val authorName: String? = null,
-    thumbhash: String? = null,
-) : MediaPreloadedContent(localFile, description, mimeType, isVerified, dim, blurhash, uri, thumbhash = thumbhash)

commons/src/jvmAndroid/kotlin/com/vitorpamplona/amethyst/commons/richtext/MediaLocalContent.kt

@@ -0,0 +1,72 @@
+/*
+ * 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.commons.richtext
+
+import androidx.compose.runtime.Immutable
+import com.vitorpamplona.quartz.nip94FileMetadata.tags.DimensionTag
+import java.io.File
+
+// Locally-cached media content. Lives in jvmAndroid because java.io.File is
+// JVM-only; iOS support will arrive when we either swap to okio.Path or pull
+// these classes back into commonMain behind an expect/actual File abstraction.
+// URL-based media classes (MediaUrlImage, MediaUrlVideo, …) remain in
+// commonMain in MediaContentModels.kt.
+
+@Immutable
+abstract class MediaPreloadedContent(
+    val localFile: File?,
+    description: String? = null,
+    val mimeType: String? = null,
+    val isVerified: Boolean? = null,
+    dim: DimensionTag? = null,
+    blurhash: String? = null,
+    val uri: String,
+    val id: String? = null,
+    thumbhash: String? = null,
+) : BaseMediaContent(description, dim, blurhash, thumbhash) {
+    fun localFileExists() = localFile != null && localFile.exists()
+}
+
+@Immutable
+class MediaLocalImage(
+    localFile: File?,
+    mimeType: String? = null,
+    description: String? = null,
+    dim: DimensionTag? = null,
+    blurhash: String? = null,
+    isVerified: Boolean? = null,
+    uri: String,
+    thumbhash: String? = null,
+) : MediaPreloadedContent(localFile, description, mimeType, isVerified, dim, blurhash, uri, thumbhash = thumbhash)
+
+@Immutable
+class MediaLocalVideo(
+    localFile: File?,
+    mimeType: String? = null,
+    description: String? = null,
+    dim: DimensionTag? = null,
+    blurhash: String? = null,
+    isVerified: Boolean? = null,
+    uri: String,
+    val artworkUri: String? = null,
+    val authorName: String? = null,
+    thumbhash: String? = null,
+) : MediaPreloadedContent(localFile, description, mimeType, isVerified, dim, blurhash, uri, thumbhash = thumbhash)