Customize desktop status bar (rebased #4152) / 自定义桌面底部信息栏

[esengine]

Rebases #4152 onto current main-v2 and resolves the conflicts so it can land. All credit to @SivanCola — this is their work; I'm only carrying the rebase across because #4071 and #4151 moved the shared frontend files after the PR was opened and the conflicts were blocking auto-merge.

Original PR: #4152

Summary

• Add a desktop status bar style setting for text or icon labels.
• Add a collapsible status bar item editor with visibility toggles, arrow ordering, drag reordering, and insertion-line feedback.
• Add a per-turn turn_cost status item and clarify the cumulative item as session cost.

Conflict resolution

• lib/bridge.ts, config/render_test.go: additive import merges (kept normalizeTokenMode from Add token economy composer mode / 增加省 token 协作模式 #4151 and reflect/path/filepath from both sides).
• components/SettingsPanel.tsx: kept both the notification-sound field (feat: 通知音效系统 — 生成完成 + 等待操作提示音 #4176) and the new status-bar fields. The two happened to share an identical trailing </div></SettingsField> close that git factored out of the hunk, so I re-added the notification-sound field's own close to keep the JSX balanced.

Verification (local)

• go test ./internal/config — green
• go build ./... (root + desktop/) — green
• pnpm --dir desktop/frontend typecheck — clean apart from the usual ungenerated-wailsjs binding errors that wails generate resolves in CI
• The two desktop test failures seen locally (TestUpdateMCPServerSplitsPastedCommandLine TempDir-cleanup flake; TestAddSkillPathRestoresConventionRootWithoutCustomPath picking up the machine's real ~/.agents/skills) reproduce on clean main-v2 and are unrelated to this change.

Closes #4152