Tighten composer layout and visual hierarchy

[dovvnloading]

Summary

• Remove the redundant LOCAL ENGINE badge from the composer utility row.
• Group model metadata, transient status, and character count into one compact right-aligned cluster.
• Tighten the composer island width, padding, row heights, textarea spacing, and mobile dimensions.
• Keep idle controls neutral and reserve the warm accent for an actionable send state.
• Tone down model-menu icon/selection colors and reduce option density.
• Add a regression test for the quieter utility row and update the UI audit.

Why

The composer is Cortex's primary control, but its previous utility row introduced too many labels, colors, and spacing changes at once. The result felt busy instead of deliberate. This pass gives the message field visual priority, makes secondary state information quiet, and makes the send action legible through availability rather than permanent color.

Validation

• 45 frontend component tests (single-worker run)
• 6 Playwright browser flows
• Frontend typecheck, lint, and production build
• Fresh Windows package build succeeded
• Packaged launch returned GET /api/v1/health/ready with HTTP 200
• Production bundle contains no removed LOCAL ENGINE badge
• git diff --check clean

Scope note

The existing user-owned Cortex.pyproj worktree change was intentionally excluded. This PR is based on the already-merged UI and starter-removal changes from PRs #66 and #67.