Add live SFTPGo WebDAV test (real 2nd WebDAV server via dav.khodak.me)

Tests the app's SFTPGo provider (WebDavProvider) end-to-end against a real
SFTPGo server over its exposed WebDAV URL: connect, mkdir, atomic upload,
list, download, overwrite, non-ASCII filename, delete. Validates the WebDAV
code path against a non-Nextcloud server. Creds via -e davUrl/davUser/davPass.

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

@@ -0,0 +1,68 @@
+package com.syncflow
+
+import androidx.test.ext.junit.runners.AndroidJUnit4
+import androidx.test.platform.app.InstrumentationRegistry
+import com.syncflow.data.providers.webdav.WebDavProvider
+import com.syncflow.domain.model.CloudAccount
+import com.syncflow.domain.model.ProviderType
+import kotlinx.coroutines.runBlocking
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertTrue
+import org.junit.Assume.assumeTrue
+import org.junit.Test
+import org.junit.runner.RunWith
+import java.io.ByteArrayInputStream
+import java.io.ByteArrayOutputStream
+
+/**
+ * Live test of the app's SFTPGo provider (which is WebDavProvider) against a real SFTPGo
+ * server over its externally-exposed WebDAV URL. Validates the provider against a different
+ * WebDAV implementation than Nextcloud. Creds via -e davUrl/davUser/davPass; skips otherwise.
+ */
+@RunWith(AndroidJUnit4::class)
+class SftpgoWebDavTest {
+
+    private val args = InstrumentationRegistry.getArguments()
+
+    private fun provider() = WebDavProvider(
+        CloudAccount(
+            id = 1, displayName = "sftpgo", email = null, providerType = ProviderType.SFTPGO,
+            credentialJson = """{"username":"${args.getString("davUser")}","password":"${args.getString("davPass")}"}""",
+            serverUrl = args.getString("davUrl"), port = null,
+        ),
+    )
+
+    @Test fun sftpgoWebDavRoundTrip() = runBlocking {
+        assumeTrue("davUrl/davUser/davPass required", args.getString("davUrl") != null)
+        val p = provider()
+        val dir = "SyncFlowDav_${System.currentTimeMillis()}"
+        try {
+            assertTrue("testConnection", p.testConnection().isSuccess)
+            assertTrue("mkdir", p.createDirectory(dir).isSuccess)
+
+            // upload (atomic temp + MOVE), list, download — with a non-ASCII payload
+            val body = "sftpgo webdav round-trip ✓ café".toByteArray()
+            assertTrue("upload", p.uploadFile(ByteArrayInputStream(body), "$dir/f.txt", body.size.toLong()).isSuccess)
+            assertTrue("f.txt" in p.listFiles(dir).getOrThrow().map { it.name })
+            val out = ByteArrayOutputStream(); p.downloadFile("$dir/f.txt", out).getOrThrow()
+            assertEquals("sftpgo webdav round-trip ✓ café", out.toString("UTF-8"))
+
+            // overwrite via atomic temp+MOVE
+            val v2 = "updated-content".toByteArray()
+            assertTrue(p.uploadFile(ByteArrayInputStream(v2), "$dir/f.txt", v2.size.toLong()).isSuccess)
+            val out2 = ByteArrayOutputStream(); p.downloadFile("$dir/f.txt", out2).getOrThrow()
+            assertEquals("updated-content", out2.toString("UTF-8"))
+
+            // non-ASCII / special filename (the URL/MOVE-header encoding fix)
+            val special = "café & rapport (1).txt"
+            assertTrue(p.uploadFile(ByteArrayInputStream("x".toByteArray()), "$dir/$special", 1).isSuccess)
+            assertTrue(special in p.listFiles(dir).getOrThrow().map { it.name })
+
+            // delete
+            assertTrue(p.deleteFile("$dir/f.txt").isSuccess)
+            assertTrue("f.txt" !in p.listFiles(dir).getOrThrow().map { it.name })
+        } finally {
+            runCatching { p.deleteFile(dir) }
+        }
+    }
+}