refactor: KMP URL validation + move UrlInfoItem to jvmAndroid

Clears the two java.net.* importers from commons/commonMain.

- Adds expect fun isValidUrl(url: String?): Boolean in
  commons/commonMain/util/. The jvmAndroid actual preserves the
  exact JVM semantics (URI.toURL() + the same 3 catch arms);
  iOS actual will use NSURL when the target lands.
- RichTextParser.isValidURL becomes a thin wrapper around
  isValidUrl. Keeps the existing static call site so callers in
  the Android app and Desktop need no change.
- UrlInfoItem.kt (link-preview model that wraps URI) moves to
  jvmAndroid; its only consumers are the Android link-preview
  pipeline (HtmlCharsetParser, UrlPreviewState, UrlPreviewCard),
  which already live outside commonMain.

commons/commonMain is now down to 3 java.* importers: Note
(BigDecimal) and the two SortedSet-based observables.

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

@@ -22,6 +22,7 @@ package com.vitorpamplona.amethyst.commons.richtext
 
 import com.vitorpamplona.amethyst.commons.emojicoder.EmojiCoder
 import com.vitorpamplona.amethyst.commons.model.ImmutableListOfLists
+import com.vitorpamplona.amethyst.commons.util.isValidUrl
 import com.vitorpamplona.quartz.experimental.inlineMetadata.Nip54InlineMetadata
 import com.vitorpamplona.quartz.nip30CustomEmoji.CustomEmoji
 import com.vitorpamplona.quartz.nip31Alts.AltTag
@@ -40,9 +41,6 @@ import kotlinx.collections.immutable.persistentListOf
 import kotlinx.collections.immutable.toImmutableList
 import kotlinx.collections.immutable.toImmutableMap
 import kotlinx.collections.immutable.toPersistentList
-import java.net.MalformedURLException
-import java.net.URI
-import java.net.URISyntaxException
 import kotlin.coroutines.cancellation.CancellationException
 
 class RichTextParser {
@@ -489,21 +487,7 @@ class RichTextParser {
             return pdfExtensions.any { removedParamsFromUrl.endsWith(it) }
         }
 
-        fun isValidURL(url: String?): Boolean =
-            try {
-                if (url != null) {
-                    URI(url).toURL()
-                    true
-                } else {
-                    false
-                }
-            } catch (e: MalformedURLException) {
-                false
-            } catch (e: URISyntaxException) {
-                false
-            } catch (e: IllegalArgumentException) {
-                false
-            }
+        fun isValidURL(url: String?): Boolean = isValidUrl(url)
 
         fun parseImageOrVideo(fullUrl: String): BaseMediaContent {
             val removedParamsFromUrl = removeQueryParamsForExtensionComparison(fullUrl)

commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/util/UrlValidation.kt

@@ -0,0 +1,31 @@
+/*
+ * 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.util
+
+/**
+ * True iff [url] is a syntactically valid absolute URL with a recognized
+ * scheme. JVM/Android delegate to `java.net.URI(url).toURL()`; the iOS actual
+ * will use `NSURL(string:)` when that target is added.
+ *
+ * Called per-URL during feed render — actuals should keep this fast and
+ * allocation-light.
+ */
+expect fun isValidUrl(url: String?): Boolean

commons/src/jvmAndroid/kotlin/com/vitorpamplona/amethyst/commons/util/UrlValidation.jvmAndroid.kt

@@ -0,0 +1,41 @@
+/*
+ * 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.util
+
+import java.net.MalformedURLException
+import java.net.URI
+import java.net.URISyntaxException
+
+actual fun isValidUrl(url: String?): Boolean =
+    try {
+        if (url != null) {
+            URI(url).toURL()
+            true
+        } else {
+            false
+        }
+    } catch (_: MalformedURLException) {
+        false
+    } catch (_: URISyntaxException) {
+        false
+    } catch (_: IllegalArgumentException) {
+        false
+    }