feat(ui): init banner + dashboard shield favicon

[WZ]

Summary

• agent-gate init now opens with an accent-green ASCII wordmark + tagline + version line, printed to stderr so --print-config stays clean. Suppressed under --quiet and --print-config. Lipgloss handles no-color degradation for non-TTY writers.
• Dashboard ships a 64×64 SVG shield favicon (dark rounded square, gradient green silhouette, white audit-pulse line). Wired via <link rel="icon" type="image/svg+xml"> in base.html and served from the embedded static FS. /favicon.ico 302s to the SVG so legacy browser probes don't 404.

Banner preview:

   ▄▀█ █▀▀ █▀▀ █▄ █ ▀█▀     █▀▀ ▄▀█ ▀█▀ █▀▀
   █▀█ █▄█ ██▄ █ ▀█  █      █▄█ █▀█  █  ██▄
   ◆ local traffic audit gate · v0.3.1

Test plan

• go test ./internal/initwizard/... — banner unit tests (wordmark + tagline + version)
• go test ./internal/dashboard/... — favicon serves at /static/favicon.svg, /favicon.ico 302→SVG, base page includes <link rel="icon">
• go vet ./... clean
• gofmt -l . clean
• Visual: qlmanage -t -s 256 of the favicon → legible shield silhouette with audit pulse, on-brand at small sizes
• Smoke: agent-gate init --dry-run --non-interactive shows banner on stderr, stdout untouched
• Smoke: agent-gate init --print-config keeps stdout clean (banner suppressed)