feat: add custom HeaderPanel widget and switchable agent modes

Replace built-in Header with a custom HeaderPanel showing model name,
mode badge, and live token usage. Add AgentMode enum (normal/plan/auto)
with mode-aware permission gating — Plan mode restricts to read-only
tools, Auto mode auto-approves everything. Includes /mode slash command
and Ctrl+P keybinding to cycle modes.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/ui/widgets.py

@@ -11,6 +11,82 @@ from textual.widgets import Button, Input, Static
 
 from rich.text import Text
 
+from app.models.config import AgentMode
+
+
+# ---------------------------------------------------------------------------
+# Header Panel
+# ---------------------------------------------------------------------------
+
+
+class HeaderPanel(Static):
+    """Single-line header showing model name, agent mode, and token usage."""
+
+    DEFAULT_CSS = """
+    HeaderPanel {
+        dock: top;
+        height: 1;
+        background: $accent;
+        color: $text;
+        padding: 0 2;
+    }
+    """
+
+    def __init__(self, model_name: str) -> None:
+        super().__init__("")
+        self._model_name = model_name
+        self._mode: AgentMode = AgentMode.NORMAL
+        self._tokens: int = 0
+        self._budget: int = 0
+
+    def on_resize(self) -> None:
+        self._refresh_display()
+
+    def update_model(self, name: str) -> None:
+        """Update the displayed model name."""
+        self._model_name = name
+        self._refresh_display()
+
+    def update_mode(self, mode: AgentMode) -> None:
+        """Update the displayed agent mode."""
+        self._mode = mode
+        self._refresh_display()
+
+    def update_tokens(self, tokens: int, budget: int) -> None:
+        """Update the token usage display."""
+        self._tokens = tokens
+        self._budget = budget
+        self._refresh_display()
+
+    def _refresh_display(self) -> None:
+        """Rebuild the header text."""
+        left = Text.assemble(
+            ("⚡ SneakyCode", "bold"),
+            " │ ",
+            (self._model_name, "bold"),
+        )
+
+        mode_styles = {
+            AgentMode.NORMAL: ("NORMAL", "bold black on white"),
+            AgentMode.PLAN: ("PLAN", "bold black on yellow"),
+            AgentMode.AUTO: ("AUTO", "bold white on red"),
+        }
+        mode_label, mode_style = mode_styles[self._mode]
+        mode_text = Text.assemble((" ", mode_style), (mode_label, mode_style), (" ", mode_style))
+
+        right = Text(f"~{self._tokens:,} / {self._budget:,} tokens")
+
+        # Pad between sections
+        total_content = left.plain + "  " + mode_text.plain + "  " + right.plain
+        available = self.size.width if self.size.width > 0 else 80
+        gap_left = max(1, (available - len(total_content)) // 2)
+        gap_right = max(1, available - len(total_content) - gap_left)
+
+        full = Text.assemble(
+            left, " " * gap_left, mode_text, " " * gap_right, right,
+        )
+        self.update(full)
+
 
 # ---------------------------------------------------------------------------
 # Modal Dialogs
@@ -139,8 +215,6 @@ class StatusBar(Static):
 
     def __init__(self) -> None:
         super().__init__("")
-        self._tokens: int = 0
-        self._budget: int = 0
         self._iteration: int = 0
         self._max_iterations: int = 0
         self._streaming: bool = False
@@ -149,12 +223,6 @@ class StatusBar(Static):
         self._stream_tokens: int = 0
         self._active_skill: str | None = None
 
-    def update_tokens(self, tokens: int, budget: int) -> None:
-        """Update the token usage display."""
-        self._tokens = tokens
-        self._budget = budget
-        self._refresh_display()
-
     def update_iteration(self, iteration: int, max_iterations: int) -> None:
         """Update the iteration count display."""
         self._iteration = iteration
@@ -200,8 +268,6 @@ class StatusBar(Static):
             parts.append(f"{spinner} Thinking")
             if self._stream_tokens > 0:
                 parts.append(f"~{self._stream_tokens:,} tokens")
-        if self._budget > 0:
-            parts.append(f"Tokens: ~{self._tokens:,} / {self._budget:,}")
         if self._max_iterations > 0:
             parts.append(f"Iteration {self._iteration}/{self._max_iterations}")
         self.update(Text(" \u2502 ".join(parts), style="dim"))