fix: 移除遗留fmfuncs目录创建 + 清理init_service无用导入 + 文件管理器SVG图标 + 示例插件MD3改造

- init_service: 删除_load_fmfuncs方法和fmfuncs目录创建(已迁移到sdk/)
- init_service: 清理未使用的importlib.util和sys导入
- 文件管理器: 全部emoji替换为MD3 SVG矢量图标(文件夹/文件类型/右键菜单)
- 示例插件: dashboard.html改为MD3风格 CSS变量自动适配日夜主题
- 面包屑: 加底色+模糊+左右外边距
- CSS: .btn::after加pointer-events:none
- 插件开发指南: 更新2.6节MD3主题同步和完善的CSS变量/组件类参考表

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

static/web_panel/css/style.css

@@ -275,6 +275,9 @@ h3{font-size:1rem;font-weight:500;letter-spacing:.15px}
 .tab.active{background:var(--primary-container);color:var(--md-sys-color-on-primary-container)}
 .tab:hover:not(.active){color:var(--text)}
 
+/* ── Plugin page container ── */
+.plugin-page-root{font-family:inherit;color:inherit}
+
 /* ── Responsive ── */
 @media(max-width:1100px){.dash-layout{flex-direction:column;height:auto;overflow:visible}.dash-sidebar{width:100%}}
 @media(max-width:768px){.app-frame{grid-template-columns:var(--sidebar-collapsed) 1fr}.nav-label{display:none}.toggle-sidebar{display:none}}
@@ -353,6 +356,7 @@ h3{font-size:1rem;font-weight:500;letter-spacing:.15px}
 .btn::after{
   content:"";position:absolute;inset:0;background:radial-gradient(circle at center,currentColor 10%,transparent 10%);
   background-size:0 0;background-repeat:no-repeat;opacity:0;transition:background-size .4s,opacity .3s;
+  pointer-events:none;
 }
 .btn:active::after{background-size:300% 300%;opacity:.12;transition:0s}
 
@@ -443,10 +447,9 @@ h3{font-size:1rem;font-weight:500;letter-spacing:.15px}
    ═══════════════════════════════════════════ */
 .fm-container{display:flex;flex-direction:column;height:calc(100vh - var(--topbar-h) - 48px);gap:12px}
 .fm-toolbar{display:flex;align-items:center;justify-content:space-between;flex-wrap:wrap;gap:8px}
-.fm-path-bar{flex:1;min-width:0;display:flex;flex-direction:column;gap:4px}
-.fm-path-input{width:100%;padding:8px 12px;background:var(--md-sys-color-surface-container-lowest);border:1px solid var(--outline);border-radius:var(--shape-xs);color:var(--text);font-family:"JetBrains Mono",monospace;font-size:12px;outline:none;transition:border-color .2s}
+.fm-path-input{flex:1;min-width:140px;padding:8px 12px;background:var(--md-sys-color-surface-container-lowest);border:1px solid var(--outline);border-radius:var(--shape-xs);color:var(--text);font-family:"JetBrains Mono",monospace;font-size:12px;outline:none;transition:border-color .2s}
 .fm-path-input:focus{border-color:var(--primary);box-shadow:0 0 0 2px rgba(208,188,255,.15)}
-.fm-breadcrumb{display:flex;align-items:center;flex-wrap:wrap;gap:4px;overflow-x:auto;scrollbar-width:none;flex:1;min-width:0}
+.fm-breadcrumb{display:flex;align-items:center;flex-wrap:wrap;gap:4px;padding:6px 10px;margin:4px 8px 0 8px;overflow-x:auto;scrollbar-width:none;flex-shrink:0;background:var(--md-sys-color-surface-container);border-radius:var(--shape-xs);backdrop-filter:blur(8px);-webkit-backdrop-filter:blur(8px)}
 .fm-breadcrumb::-webkit-scrollbar{display:none}
 .fm-crumb{white-space:nowrap;padding:4px 10px;border-radius:var(--shape-full);cursor:pointer;font-size:.82rem;color:var(--text-dim);transition:.15s}
 .fm-crumb:hover{background:rgba(208,188,255,.1);color:var(--primary)}