style: unify the ink accent, fix text contrast, and clarify disabled states

[jibraaan]

What and why

The compact-chrome layer moved the app to an ink (near-black) palette, but several older surfaces kept the original lavender: .primary buttons, focus rings, checkboxes and the setup notes. As a result, Settings looked like a different app from the chat screen. A few states were also hard to read or misleading.

• One accent: primary buttons, focus rings and checkboxes use the ink accent.
• Disabled controls look disabled: before setup, the send button was near-black at 90% opacity and looked clickable. Disabled primary and send buttons are now neutral gray.
• Contrast: secondary text in the "Connect your Dot" card, the config notes and the permission descriptions measured about 2.4–2.7:1. It now measures 5.3:1 (WCAG AA).
• Settings: missing environment variables are shown as code.
• Sidebar: Spaces gets the same spacing as Dots (it sat flush against the Dot row), nav labels stay on one line, and zero-count badges are hidden.

This is a refinement pass, not a redesign: no copy, layout or behavior changes beyond the above. The CSS is a single appended, clearly labeled layer, following the existing pattern of appended layers. JSX changes are limited to the badge condition and the env-var code formatting.

Verification

• npm run check-format, lint, typecheck, test (164 passing) and build all pass.
• Checked in the browser at desktop and 375px widths: no horizontal overflow, and contrast measured as above.
• Not covered: views that need configured services (active chat, call) weren't visually reviewed.

Independent of the dark-mode PR; either can merge first.

🤖 Generated with Claude Code