M2: build out task list, detail & edit screens

Replace the base scaffolds with the real Material 3 Expressive UI on the
existing M1 ViewModels.

Task list: due-date section headers (collapsible Completed), grouped tonal
rows with a list-colour accent bar, swipe-to-complete / -delete, inline add,
list-name chip and subtask "done/total" chip in mixed views (children folded
into their parent). New pure TaskSections grouping + unit test.

Detail: each fact its own tonal card with a leading icon (Calendula pattern) —
when/list/priority/progress/description; progress shows only with subtasks.
Subtasks are a connected grouped run whose first segment is the expand toggle,
with an accent-tinted inline add row; completed subtasks sink to the bottom.

Edit: title, description, list dropdown, start/due date-time + all-day,
priority segmented buttons, reminder offset, validation; IME auto-scroll.

Extract GroupedSurface from GroupedRow so the connected-row look is reusable
at any width; add ListNameChip + date-time format/picker helpers.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/src/test/java/de/jeanlucmakiola/floret/domain/TaskSectionsTest.kt

@@ -0,0 +1,47 @@
+package de.jeanlucmakiola.floret.domain
+
+import com.google.common.truth.Truth.assertThat
+import org.junit.jupiter.api.Test
+import kotlin.time.Instant
+
+class TaskSectionsTest {
+
+    private val dayMs = 86_400_000L
+    private val todayStart = Instant.fromEpochMilliseconds(1000 * dayMs)
+    private val todayEnd = Instant.fromEpochMilliseconds(1001 * dayMs)
+
+    private fun at(millis: Long) = Instant.fromEpochMilliseconds(millis)
+    private fun sectionOf(task: Task) = TaskSections.sectionOf(task, todayStart, todayEnd)
+
+    @Test
+    fun `buckets by due relative to today`() {
+        assertThat(sectionOf(testTask(due = at(1000 * dayMs - 1)))).isEqualTo(TaskSection.OVERDUE)
+        assertThat(sectionOf(testTask(due = at(1000 * dayMs + 1)))).isEqualTo(TaskSection.TODAY)
+        assertThat(sectionOf(testTask(due = at(1001 * dayMs + 1)))).isEqualTo(TaskSection.UPCOMING)
+        assertThat(sectionOf(testTask(due = null))).isEqualTo(TaskSection.NO_DATE)
+    }
+
+    @Test
+    fun `completed always lands in completed regardless of due`() {
+        val overdueButDone = testTask(status = TaskStatus.COMPLETED, due = at(1000 * dayMs - 1))
+        assertThat(sectionOf(overdueButDone)).isEqualTo(TaskSection.COMPLETED)
+    }
+
+    @Test
+    fun `of returns only non-empty sections in fixed order`() {
+        val tasks = listOf(
+            testTask(id = 1, due = at(1001 * dayMs + 1)),   // upcoming
+            testTask(id = 2, due = at(1000 * dayMs - 1)),   // overdue
+            testTask(id = 3, status = TaskStatus.COMPLETED), // completed
+        )
+        val sections = TaskSections.of(tasks, todayStart, todayEnd)
+        assertThat(sections.map { it.section })
+            .containsExactly(TaskSection.OVERDUE, TaskSection.UPCOMING, TaskSection.COMPLETED)
+            .inOrder()
+    }
+
+    @Test
+    fun `empty input yields no sections`() {
+        assertThat(TaskSections.of(emptyList(), todayStart, todayEnd)).isEmpty()
+    }
+}