Build the unified settings shell for providers, policies, and storage

[KSemenenko]

Problem

dotPilot needs one coherent settings surface so operators can manage provider connections, runtime policies, and local storage from the app.

Scope

• Track the in-app settings shell that will host provider, toolchain, policy, and storage configuration
• Define navigation and grouping for the most important control-plane settings

Out of scope

• Detailed provider health checks that belong in the Toolchain Center
• Session-specific instruction editing that belongs in session composition flows

Implementation notes

• Keep settings coherent with the current desktop shell
• Avoid scattering critical configuration across unrelated dialogs
• Ensure policy and storage settings are visible early in product planning

Definition of Done

• The issue defines the first-class settings areas and their boundaries
• The settings shell is described as a product surface, not a catch-all backlog bucket

Verification

• Review the issue against the feature spec and current shell layout

Dependencies

• Parent epic: [Epic] Replace the static prototype with a real desktop workbench #13
• Related epic: [Epic] Build the provider toolchain center for Codex, Claude Code, and GitHub Copilot #14