feat: port Window Controls Overlay + markdown file link UX (upstream #1969, #1956)

[tyulyukov]

Summary

Ports two upstream commits from the next tier of t3code port work onto MarCode:

• Window Controls Overlay (dff8784a, upstream window controls overlay (windows&linux) pingdotgg/t3code#1969) — native Windows/Linux titlebar overlay so maximize/minimize/close buttons sit inside the app chrome, while keeping macOS's hiddenInset + traffic-light offset intact.
• Markdown file link UX (68061af0, upstream Improve markdown file link UX pingdotgg/t3code#1956) — chat messages render file references as monospaced chips with workspace-relative labels, icons, and hover tooltips. Changed-file previews in work-log entries are also truncated to workspace-relative form.

Upstream's Claude Opus 4.7 port (3e07f5a6) was checked during planning and is already in main via 24dc316a; cherry-pick skipped (re-applying it would overwrite MarCode's claude-first defaults).

Key reconciles (MarCode divergences preserved)

• Sidebar.tsx — macOS traffic-light hack preserved. Inline style={{ paddingLeft: 58 }} converted to conditional pl-[58px] class so the wco:pl-[calc(env(titlebar-area-x)+1em)] variant can override on Windows/Linux.
• apps/desktop/src/main.ts — merged upstream's getWindowTitleBarOptions / syncWindowAppearance / syncAllWindowAppearance / nativeTheme.on("updated", ...) helpers with MarCode's existing captureWindowState / saveWindowState / window-state persistence. MarCode's createWindow(options?: { deferLoad?: boolean }) signature + resolveWindowBounds preserved.
• ChatView.tsx — upstream's discriminated-union ChatViewProps (with routeKind/draftId/onDiffPanelOpen) not adopted, since MarCode uses separate route files for draft vs server threads. Added only the new reserveTitleBarControlInset?: boolean prop. Kept MarCode's collapsed-sidebar pl-[90px] macOS traffic-light hack in the header and layered upstream's wco:h-[...] + wco:pr-[...] variants on top.
• MessagesTimeline.tsx — MarCode keeps work-group rendering inline in renderRowContent (upstream extracted it to WorkGroupSection). Applied upstream's intent surgically: imported formatWorkspaceRelativePath, threaded workspaceRoot into SimpleWorkEntryRow + workEntryPreview, wrapped changed-file chips. No structural refactor.
• MessagesTimeline.test.tsx — MarCode's two existing tests preserved; upstream's new "formats changed file paths from the workspace root" test appended in MarCode's inline-props style (MarCode doesn't use a `buildProps()` helper).

Test plan

• `bun --filter @marcode/web typecheck`
• `bun --filter @marcode/desktop typecheck`
• `bun --filter @marcode/web test` — 1011/1011 passed (95 files)
• `bun --filter @marcode/desktop test` — 82/82 passed (13 files)
• Regression guard: `service.notification-wiring` — 4/4 passed
• Regression guard: `windowState.integration-guard` — 8/8 passed
• Windows/Linux smoke test — we don't run CI on those Electron targets, so the WCO behavior ships "blind" with confidence that upstream tested it. Anyone on Win/Linux should verify native titlebar controls render inline with the app chrome.
• macOS smoke: sidebar logo still clears the traffic lights in windowed mode and shifts flush-left in fullscreen; chat header/diff panel/settings heights unchanged.
• Chat smoke: file references in assistant responses render as monospaced chips with workspace-relative labels + absolute-path tooltips; clicking opens the file.

Notes

• Both cherry-picks preserve upstream authorship (Taras Fomin, legs).
• Branch isolated from `main`; no force-push risk.

🤖 Generated with Claude Code