fix: restore essential UI guidance

Settings navigation and several workspace surfaces had lost context that helps users scan, understand, and operate them. Restore concise bilingual descriptions, workflow cues, and visual hierarchy for the welcome message, composer, activity history, knowledge workflows, Magic Notes, assistant workbar, Runtime settings, and channel projects while keeping decorative or duplicate copy removed.

Release note: 恢复设置菜单副标题、新对话引导及知识库、运行记录、魔法笔记和助手工作栏中的必要说明，提升功能可发现性与页面信息层级。

src/renderer/src/SettingsPanel.tsx

@@ -1795,6 +1795,7 @@ export function SettingsPanel({
                   <X aria-hidden="true" size={19} />
                 </button>
               }
+              description={t('center.description')}
               headingId="settings-title"
               title={t('center.title')}
             />
@@ -1830,6 +1831,11 @@ export function SettingsPanel({
                 <strong>
                   {t(`categories.${category.translationKey}.label`)}
                 </strong>
+                <small>
+                  {t(
+                    `categories.${category.translationKey}.navigationDescription`
+                  )}
+                </small>
               </button>
             ))}
           </nav>
@@ -2129,6 +2135,9 @@ export function SettingsPanel({
               </div>
               <details className="settings-section">
                 <summary>{t('runtime.advanced')}</summary>
+                <p className="settings-panel__description">
+                  {t('runtime.opencode.advancedDescription')}
+                </p>
                 <fieldset className="runtime-source-options">
                   <legend>{t('runtime.sourceLegend')}</legend>
                   <label>
@@ -2357,6 +2366,9 @@ export function SettingsPanel({
               </div>
               <details className="settings-section">
                 <summary>{t('runtime.advanced')}</summary>
+                <p className="settings-panel__description">
+                  {t('runtime.continue.advancedDescription')}
+                </p>
                 <fieldset className="runtime-source-options">
                   <legend>{t('runtime.sourceLegend')}</legend>
                   <label>