dashboard: Add per-folder config with workspace observation

Dashboard now switches config (tools, automations, agents, state) when
the user changes the active folder via the title bar dropdown. Observes
workspace active_worktree_override changes and reloads from the folder's
config/ directory if present. Sticky behavior: folders without config
leave the dashboard unchanged.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: 2 people