feat(v0.4.3): TUI 命令 Tab 补全

CommandSuggester 实现 Textual Suggester API:
- 根据已注册命令列表提供前缀匹配补全
- 前缀无匹配时 fallback 到包含匹配
- 按长度排序，优先最短匹配
- 在 Input placeholder 提示 'Tab 补全'

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

services/tui_service.py

@@ -9,6 +9,8 @@ from textual.app import App
 from textual.containers import Container, ScrollableContainer, Horizontal
 from textual.widgets import Static, Input, Header, Footer, LoadingIndicator
 from textual.reactive import reactive
+from textual.suggester import Suggester
+from textual.suggestion import Suggestion
 from typing import List, Dict
 import asyncio
 from datetime import datetime
@@ -493,6 +495,37 @@ class PluginStatusPanel(Static):
             pass
 
 
+class CommandSuggester(Suggester):
+    """命令补全 — 根据已注册命令提供 Tab 补全建议"""
+
+    def __init__(self, command_service=None):
+        self._cmd_svc = command_service
+
+    def set_command_service(self, svc):
+        self._cmd_svc = svc
+
+    async def get_suggestion(self, value: str) -> Suggestion | None:
+        """根据当前输入返回匹配的命令建议"""
+        if not value or not self._cmd_svc:
+            return None
+        value_lower = value.lower().strip()
+        commands = getattr(self._cmd_svc, "commands", {})
+        # 优先前缀匹配
+        candidates = sorted(
+            [n for n in commands if n.startswith(value_lower)],
+            key=len,
+        )
+        if not candidates:
+            candidates = sorted(
+                [n for n in commands if value_lower in n],
+                key=len,
+            )
+        if candidates:
+            cmd = candidates[0]
+            return Suggestion(cmd[len(value_lower):])
+        return None
+
+
 class TUIFramework(App):
     """TUI框架应用"""
     def __init__(self, config, log_service, command_service, plugin_service=None):
@@ -623,7 +656,12 @@ class TUIFramework(App):
             self.message_display,
             id="message-area"
         )
-        self.command_input = Input(placeholder="输入指令...", id="command-input")
+        self.command_suggester = CommandSuggester(self.command_service)
+        self.command_input = Input(
+            placeholder="输入指令...  Tab 补全",
+            suggester=self.command_suggester,
+            id="command-input",
+        )
         yield Container(
             self.command_input,
             id="input-area"