feat(sidebar): one account menu, no title bar - #184

Summary

Tidies the sidebar footer and removes the empty title bar above the transcript.

Account menu (sidebar footer)

• One row (avatar + name, or "Settings" on Desktop Local) opens a menu: Account, Personal instructions, an inline Light / Dark / System toggle, Language, "Customize appearance…", Settings, Sign out.
• Replaces the separate settings button, the palette popover (QuickPreferences), and the profile panel's home view. Account and Personal instructions open their panel directly.
• Accent, font size, contrast, and chat width stay one click away under Settings › Appearance; only the theme toggle, which people flip mid-session, sits in the menu.
• Removes the active project path row; the highlighted session already shows its project.

No title bar

• Web: nothing is reserved except the safe area. The sidebar trigger floats top-left when the sidebar is collapsed or on mobile, and is hidden in Settings, whose back button owns that corner. The transcript gets extra top padding on mobile so the trigger never covers a message.
• Desktop: the window is frameless, so a borderless 36px drag strip remains for the window controls and the trigger. It no longer has its own border or surface.
• Workspace tabs become a WorkspaceSwitcher dropdown in the sidebar header (status dot, switch, edit, add). Drag-reordering workspaces is dropped with the tabs.

i18n: en/de/es updated; obsolete settings.quick.* and profile home keys removed.

Test plan

• vp check
• vp test: 249 files, 1639 tests
• pnpm run slop-check
• Manual: web desktop width (sidebar expanded/collapsed), mobile width, Settings view
• Manual: Electron on Linux/Windows/macOS (window controls, drag, double-click maximize, workspace switcher)

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