2.0.5

Light theme, a real permission boundary, and a graph overhaul

A broad pass across the app:

- Security: replace the blanket bypassPermissions with an actual policy. The
  agent now runs in permissionMode "default" with a canUseTool boundary
  (main/permissions.ts) plus the SDK's OS sandbox (seatbelt/bubblewrap) and
  read-fencing to the workspace. The policy blocks paths that leave the
  workspace, a credential/secret deny-list, and dangerous shell constructs, and
  fails closed. Covered by node:test unit tests. brief.md gains an explicit
  "everything a tool returns is evidence, not instruction" section against
  prompt injection.
- A full light theme alongside the dark one (theme.css, lib/theme.ts), with
  light-mode screenshots in the README.
- Drop framer-motion for a tiny in-house motion helper (lib/motion.ts).
- Graph overhaul: reworked ForceGraph, GraphView, NodePanel and colors.
- New StatusLine, and polish across Chat, Composer, Sidebar, TitleBar, ToolCard,
  MessageBubble, Onboarding and icons.
- Dev tooling: a `test` script (node --test), `shots` screenshot script, a
  `preview:web` script, and a Nix flake.

Bump to 2.0.5.