fix(i18n): replace hardcoded Chinese strings in Session Manager

- Add i18n keys for relative time (justNow, minutesAgo, hoursAgo, daysAgo)
- Add i18n keys for role labels (roleUser, roleSystem, roleTool)
- Add i18n keys for UI elements (tocTitle, searchSessions, clickToCopyPath)
- Update formatRelativeTime and getRoleLabel to accept t function
- Add useTranslation hook to SessionToc component

src/components/sessions/SessionManagerPage.tsx

@@ -288,7 +288,7 @@ export function SessionManagerPage() {
                             <Search className="size-3.5" />
                           </Button>
                         </TooltipTrigger>
-                        <TooltipContent>搜索会话</TooltipContent>
+                        <TooltipContent>{t("sessionManager.searchSessions")}</TooltipContent>
                       </Tooltip>
 
                       <Select
@@ -482,7 +482,7 @@ export function SessionManagerPage() {
                                   {selectedSession.projectDir}
                                 </p>
                                 <p className="text-muted-foreground mt-1">
-                                  点击复制路径
+                                  {t("sessionManager.clickToCopyPath")}
                                 </p>
                               </TooltipContent>
                             </Tooltip>