test(compose): add RichTextEditor unit + ComposeScreen UI coverage (#176)

Closes the #36 test-coverage gap left after the rich-text editor shipped:

- RichTextEditorTest.kt (new JVM unit test, 20 cases): exercises the
  Compose-editor glue in RichTextEditor.kt that had no direct coverage -
  applyStyle/applyBlock/applyLink, the AnnotatedString.toRichContent() <->
  RichTextContent.toAnnotatedString() round trip across every span/link/
  alignment/image/baseStyle channel, and the isStyled/hasBlock predicate
  FormattingToolbar uses to light up its buttons. All plain TextFieldValue/
  AnnotatedString/Color types, so it runs on the JVM with no emulator.
  applyBlock/applyLink go from private to internal so the test can reach
  them directly, mirroring applyStyle's existing internal visibility.

- ComposeScreenTest.kt (androidTest, following this file's existing
  createAndroidComposeRule + fake-repository harness): one case taps the
  bullet-list toolbar button and asserts the sent message carries the
  <ul><li> HTML (block markers apply to the caret's line, so no fragile
  on-device range selection is needed); another asserts every toolbar
  button's click-action label matches its string resource, verifying the
  accessibility claim (the labels are onClickLabel, not contentDescription).

Headings remain deliberately out of scope per the ticket - no model/
toolbar changes here.

Closes #36

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

app/src/androidTest/kotlin/org/libremail/ui/compose/ComposeScreenTest.kt

@@ -3,6 +3,7 @@ package org.libremail.ui.compose
 
 import android.Manifest
 import androidx.activity.ComponentActivity
+import androidx.compose.ui.semantics.SemanticsActions
 import androidx.compose.ui.test.assertIsDisplayed
 import androidx.compose.ui.test.assertIsEnabled
 import androidx.compose.ui.test.assertIsNotEnabled
@@ -169,6 +170,59 @@ class ComposeScreenTest {
         assertEquals("bcc@example.com", sent.bcc)
     }
 
+    @Test
+    fun formattingToolbar_bulletButtonMarksTheLineAndSendsItAsHtml() {
+        val mailRepository = FakeMailRepository()
+        setContent(mailRepository)
+
+        composeTestRule.onNodeWithText(string(R.string.compose_to)).performTextInput("you@example.com")
+        composeTestRule.onNodeWithText(string(R.string.compose_body)).performTextInput("Buy milk")
+        // The bullet-list button is deliberately chosen over the inline styles (bold/italic): block
+        // markers apply to the caret's whole line, so the end-of-text caret that performTextInput
+        // leaves is enough - no on-device range selection (which is unreliable in instrumented tests)
+        // is needed to prove that a toolbar tap flows real formatting into the sent message's HTML.
+        // "•" is the bullet button's own (untranslated) glyph label - see FormattingToolbar.
+        composeTestRule.onNodeWithText("•").performClick()
+        composeTestRule.onNodeWithContentDescription(string(R.string.action_send)).performClick()
+
+        composeTestRule.waitUntil(timeoutMillis = 5_000) { mailRepository.sentMessages.isNotEmpty() }
+        val sent = mailRepository.sentMessages.single()
+        // Plaintext keeps the readable "• " marker; the HTML part carries the real <ul>/<li> structure.
+        assertEquals("• Buy milk", sent.body)
+        assertTrue(
+            "expected bullet-list html, got ${sent.bodyHtml}",
+            sent.bodyHtml?.contains("<ul><li>Buy milk</li></ul>") == true,
+        )
+    }
+
+    @Test
+    fun formattingToolbar_buttonsCarryOnClickLabelsForAccessibility() {
+        setContent()
+
+        // Every toolbar button (see FormattingToolbar in RichTextEditor.kt) is a plain clickable Box with
+        // a bare glyph Text as its only visible content, so TalkBack relies entirely on the click action's
+        // label (there is no separate contentDescription) to announce what the button does.
+        val buttons = listOf(
+            "B" to R.string.format_bold,
+            "I" to R.string.format_italic,
+            "U" to R.string.format_underline,
+            "•" to R.string.format_bullet_list,
+            "1." to R.string.format_numbered_list,
+            "❝" to R.string.format_quote,
+            "🔗" to R.string.format_link,
+        )
+        buttons.forEach { (glyph, descriptionRes) ->
+            val config = composeTestRule.onNodeWithText(glyph).fetchSemanticsNode().config
+            val clickLabel = if (config.contains(SemanticsActions.OnClick)) {
+                config[SemanticsActions.OnClick].label
+            } else {
+                null
+            }
+            val message = "toolbar button \"$glyph\" is missing its accessibility label"
+            assertEquals(message, string(descriptionRes), clickLabel)
+        }
+    }
+
     /** Matches the editable field labelled [labelRes] but not the collapsed Cc/Bcc link buttons. */
     private fun editableField(labelRes: Int) = composeTestRule.onNode(hasText(string(labelRes)) and hasSetTextAction())
 }