feat(tui-v3): Shift+Enter on Windows + logical-line arrow navigation

- _ptk_keypress_to_bytes 在 Windows 上对 Enter 收到 \r 时用
  GetAsyncKeyState(VK_SHIFT) 物理检测 Shift,按下时返回 \n 以触发换行
  (PTK 在某些 Windows 终端区分不出 Shift+Enter 与裸 Enter)。
- 新增 _line_region / _logical_visual_range 辅助函数,↑/↓ 按键:
  不在该逻辑行的视觉首/末行 → 视觉滚行;在视觉首行且光标在行首 →
  历史导航,否则先跳逻辑行首/尾,下次按键再跨行/进历史。多行粘贴
  内部导航更符合直觉。

Refs:
- Shift+Enter 物理检测 from upstream PR #519 by @jlu005807
  https://github.com/lsdefine/GenericAgent/pull/519
- 多行输入逻辑行边界导航思路 from upstream PR #520 by @jlu005807
  https://github.com/lsdefine/GenericAgent/pull/520

frontends/tui_v3.py

@@ -807,7 +807,12 @@ def _ptk_keypress_to_bytes(kp) -> bytes:
         return any(n in a for a in aliases for n in needles)
 
     # Enter submits; Ctrl+J / Shift+Enter insert newline when PTK can distinguish.
+    # Windows terminals send \r for both Enter/Shift+Enter — detect Shift physically.
     if has('controlm', 'c-m') or key_s in ('\r', '\n'):
+        if _IS_WINDOWS:
+            import ctypes
+            if ctypes.windll.user32.GetAsyncKeyState(0x10) & 0x8000:
+                return b'\n'
         return b'\r'
     if has('controlj', 'c-j', 's-enter', 'shift-enter'):
         return b'\n'
@@ -2542,6 +2547,27 @@ class SB:
                 return i, p - st
         return len(segs) - 1, len(segs[-1][1])
 
+    def _line_region(self, pos: int | None = None) -> tuple[int, int, int, int]:
+        """(行号, 总行数, 行起始偏移, 行结束偏移) 基于逻辑行（\\n分割）"""
+        p = self.pos if pos is None else pos
+        ls = self.buf.rfind('\n', 0, p) + 1
+        le = self.buf.find('\n', p)
+        if le == -1:
+            le = len(self.buf)
+        line_no = self.buf[:p].count('\n')
+        total = self.buf.count('\n') + 1
+        return line_no, total, ls, le
+
+    def _logical_visual_range(self, segs, line_no):
+        """返回第 line_no 个逻辑行在 segs 中的 (first_vi, last_vi)"""
+        lines = self.buf.split('\n')
+        iw = max(1, _term()[0] - 6)
+        first = 0
+        for i in range(line_no):
+            first += max(1, len(_wrap_cells(lines[i], iw)))
+        cnt = max(1, len(_wrap_cells(lines[line_no], iw)))
+        return first, first + cnt - 1
+
     def _cur_v(self, d: int) -> None:
         """↑/↓ roam by VISUAL row (a long single-line paste wraps to many rows
         yet stays one logical line — must still roam). At the top/bottom visual
@@ -5157,7 +5183,23 @@ class SB:
                         self._pending_drain_t = 0.0
                     self._render_live()
                 else:
-                    self._sel = None; self._cur_v(-1)
+                    self._sel = None
+                    line_no, total, ls, le = self._line_region()
+                    segs = self._segs(max(1, _term()[0] - 6))
+                    vi, _ = self._seg_at(segs)
+                    first_vi, _ = self._logical_visual_range(segs, line_no)
+                    if vi == first_vi:          # 在视觉首行
+                        if line_no == 0:
+                            if self.pos == ls:
+                                self._nav_hist(-1)
+                            else:
+                                self.pos = ls
+                        elif self.pos == ls:
+                            self._cur_v(-1)     # 已在行首 → 正常上移
+                        else:
+                            self.pos = ls       # 跳到该行行首
+                    else:
+                        self._cur_v(-1)
             elif o == 0x13:                       # Ctrl+S stash/restore draft
                 self._stash_draft()
             elif o == 0x0e:                       # ↓ visual-row down (history at bottom)
@@ -5165,7 +5207,23 @@ class SB:
                     n = len(self._cmd_matches(self.buf))
                     self._palette_sel = min(n - 1, self._palette_sel + 1) if n else 0
                 else:
-                    self._sel = None; self._cur_v(1)
+                    self._sel = None
+                    line_no, total, ls, le = self._line_region()
+                    segs = self._segs(max(1, _term()[0] - 6))
+                    vi, _ = self._seg_at(segs)
+                    first_vi, last_vi = self._logical_visual_range(segs, line_no)
+                    if vi == last_vi:           # 在视觉末行
+                        if line_no == total - 1:
+                            if self.pos == le:
+                                self._nav_hist(1)
+                            else:
+                                self.pos = le
+                        elif self.pos == le:
+                            self._cur_v(1)      # 已在行末 → 正常下移
+                        else:
+                            self.pos = le       # 跳到该行行末
+                    else:
+                        self._cur_v(1)
             elif o == 0x02:                       # ← caret left
                 self._sel = None; self.pos = max(0, self.pos - 1)
             elif o == 0x06:                       # → caret right