Fix WebDAV upload of non-ASCII/special filenames (URL + MOVE header encoding)

Volume test (100 files) surfaced it: files with non-ASCII names (e.g. 'naïve
café.txt') failed to upload — url() built a raw string, so the MOVE Destination
header carried non-ASCII chars that OkHttp rejects. Now url() percent-encodes
each path segment via HttpUrl.addPathSegments (also covers '&', spaces, CJK).
Regression test specialAndNonAsciiNames_upload added.

app/src/androidTest/kotlin/com/syncflow/FullSyncEngineTest.kt

@@ -236,7 +236,24 @@ class FullSyncEngineTest {
         assertEquals("newer local must win", "local-newer", remoteText("$remote/n.txt"))
     }
 
-    // ── 13. Content integrity: binary-ish bytes round-trip exactly ────────────
+    // ── 13b. Special & non-ASCII filenames upload (WebDAV URL/header encoding) ─
+    @Test fun specialAndNonAsciiNames_upload() = runBlocking {
+        val (pair, local, remote) = newPair("special", SyncDirection.UPLOAD_ONLY, DeleteBehavior.KEEP)
+        write(local, "naïve café.txt", "accents")   // non-ASCII (broke MOVE Destination header)
+        write(local, "a&b (1).txt", "ampersand")     // & ( ) space
+        write(local, "日本語.txt", "cjk")              // multibyte unicode
+        write(local, "my photo.txt", "space")
+        val r = sync(pair)
+        assertEquals("all special-name files must upload", 4, r.uploaded)
+        assertEquals(0, r.failedFiles)
+        val names = remoteNames(remote)
+        assertTrue("naïve café.txt" in names)
+        assertTrue("a&b (1).txt" in names)
+        assertTrue("日本語.txt" in names)
+        assertTrue("my photo.txt" in names)
+    }
+
+    // ── 14. Content integrity: binary-ish bytes round-trip exactly ────────────
     @Test fun contentIntegrity_roundTrip() = runBlocking {
         val (pair, local, remote) = newPair("integrity", SyncDirection.TWO_WAY)
         val payload = (0..5000).joinToString("") { "Ω$it·" }

app/src/main/kotlin/com/syncflow/data/providers/webdav/WebDavProvider.kt

@@ -181,7 +181,13 @@ open class WebDavProvider(protected val account: CloudAccount) : CloudProvider {
         }
     }
 
-    protected fun url(path: String) = "$baseUrl/${path.trimStart('/')}"
+    // Build a properly percent-encoded URL. addPathSegments encodes each segment (spaces,
+    // ampersands, and — critically — non-ASCII like "café"), which keeps OkHttp from rejecting
+    // non-ASCII in the WebDAV MOVE "Destination" header and avoids malformed request URLs.
+    protected fun url(path: String): String {
+        val base = baseUrl.toHttpUrlOrNull() ?: return "$baseUrl/${path.trimStart('/')}"
+        return base.newBuilder().addPathSegments(path.trimStart('/')).build().toString()
+    }
 
     private fun parsePropfind(xml: String, parentPath: String, dropFirst: Boolean = true): List<RemoteFile> {
         val results = mutableListOf<RemoteFile>()