Make Overview the default workspace home

[tonyfresher]

Adds Overview as the default workspace home, with a built-in Views launcher and the existing widgets collected under one host-owned surface. It also brings workspace identity editing, styling, settings, hidden widgets, and creation actions into the Overview flow while preserving the proven react-grid-layout movement behavior.

Workspace
├── Overview (default)
│   ├── Views · open or create full-page tools
│   └── Widgets · inspect, hide, restore, or create widgets
├── Agent
└── Scratchpad

The custom dnd-kit canvas is deliberately excluded and remains isolated on the follow-up canvas branch.

Review closely

• Tab normalization pins Overview and removes the retired Widgets route while preserving valid saved tabs.
• New workspaces receive the host-owned Views widget; existing empty or hidden layouts stay unchanged.
• Workspace icon updates rasterize generated choices and serialize rapid actions before persistence.

Verification

• bun test — 1,465 passed, 4 skipped
• bun run typecheck:client
• bun run lint
• bun run format:check
• bun run build:client
• git diff --check
• Browser-tested Overview routing, empty states, Style, settings, icon editing, launchers, and retained RGL rendering.