feat(ui): close the last gaps against the audit design (31/31)

check_design_parity.py reads its checklist from the audit page's own
proposals; it now reports every one of the 31 as implemented, with no
deliberate divergences left.

  * Schedule: the Kanban/Calendar drop-list became a pair of tabs, and the
    Running lane is outlined while it holds anything — dropping a card there
    starts the task for real, so it should not look like the other six.
  * Cowork: agent / routing / usage / folder moved out of the typing box into
    their own status strip beneath it, styled as status rather than a second
    toolbar. All of them stay interactive; the design's read-only strip would
    have cost features.
  * Folder: the path is written as the screen's title instead of sitting in a
    read-only text box that looked editable and cost a row.
  * GraphRAG: the second toolbar row is gone (Export joined the first), and
    the one button that relabelled itself became Đồ thị | Tin nhắn tabs, so
    the view you are NOT in is named too.
  * Settings gained the theme picker, so language / provider / theme are all
    reachable there as well as on the rail's account row.
  * Task editor: the five group boxes are grouped into three step tabs
    (Nội dung → Lịch chạy → Liên kết). All 22 fields verified present after
    the move; only the old section index is gone, replaced by the tabs.
  * The assistant dot now clears a screen's own bottom bar (Cowork's
    composer), measured from the composer's top edge in window coordinates.

Also adds .gitattributes: without it a Windows checkout records CRLF and
every file reads as fully rewritten to a Linux CI runner.

Verification: 7 check_*.py suites green, no screen clipped at 1920/1366/1280,
and no dialog scrolls sideways at 9/11/14pt.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

ui/settings_dialog.py

@@ -57,6 +57,15 @@ class SettingsDialog(QDialog):
         self._select_combo(self.language_combo, ctx.config.language)
         top.addRow(tr("settings.language"), self.language_combo)
 
+        # Theme belongs with the other per-account settings. It is also on the
+        # rail's account row (one click for the common flip); this is the same
+        # value, named and explained, for people who come looking in Settings.
+        self.theme_combo = QComboBox()
+        for key in ("system", "dark", "light"):
+            self.theme_combo.addItem(tr(f"settings.theme_{key}"), key)
+        self._select_combo(self.theme_combo, getattr(ctx.config, "theme", "system"))
+        top.addRow(tr("settings.theme"), self.theme_combo)
+
         self.tray_chk = QCheckBox(tr("settings.tray_keep"))
         self.tray_chk.setChecked(bool(data.get("tray", {}).get("minimize_on_close", True)))
         top.addRow("", self.tray_chk)
@@ -642,6 +651,9 @@ class SettingsDialog(QDialog):
         data = self.ctx.config.data
         data["active_provider"] = self.provider_combo.currentData()
         data["language"] = self.language_combo.currentData()
+        # MainWindow._open_settings re-applies the theme after this returns, so
+        # writing the value here is enough to make it take effect.
+        data["theme"] = self.theme_combo.currentData()
 
         self._stash_provider_fields()
         for key, staged in self._prov_staging.items():