Co4E step config as collapsible sections; tighter Kanban lanes; Output panel fills its column

- co4e_config_panel: StepConfigPanel reorganized into four collapsible,
  borderless sections (Co ban / Model & Quyen / Skills & Tep / Agent song
  song) instead of one long form. Agent song song is its own section,
  shown only for parallel-variant steps. Fixes a QVBoxLayout without a
  trailing stretch that was handing every section an equal share of the
  scroll area's leftover height instead of sizing to content.
- schedule_task_tab / theme: Kanban board lane gutters and per-lane
  margins trimmed so the seven lanes read their card content more
  clearly on a laptop-width window.
- chat_panel / widgets: the Output Files list in Cowork/Code no longer
  stops at a fixed height with empty panel below it - it now fills the
  column down to the composer.
- composer: Attach/Send/Stop buttons match the input box's height and
  align to its top/bottom edge instead of floating centered beside it.
- app.py: the sidebar's "All projects" link reads as a link (italic,
  accent color) instead of a plain row.
- i18n: labels for the three renamed Co4E section headers (VI/EN/JA).

ui/composer.py

@@ -452,7 +452,12 @@ class Composer(QWidget):
         self.stop_btn.setObjectName("danger")
         self.stop_btn.setVisible(False)
         self.stop_btn.clicked.connect(self.stop_requested.emit)
+        # Attach pinned to the input's top edge, Send (and Stop, once a turn
+        # is running) pinned to its bottom edge — the gap between them is
+        # absorbed by this stretch instead of splitting evenly above/below
+        # the whole button column, which is what centering it did before.
         btns.addWidget(self.attach_btn)
+        btns.addStretch(1)
         btns.addWidget(self.send_btn)
         btns.addWidget(self.stop_btn)
         row.addLayout(btns)