docs: promote Homebrew to primary installation path across docs and website

[jatinkrmalik]

Summary

• Homebrew is now the recommended and primary installation method across all documentation and the marketing website
• Website hero section gets a "Quick Install" button that reveals a copyable terminal with brew commands
• All installation ordering is consistent: Homebrew → DMG → Build from Source

Changes

README.md

• Quick Start reordered: Option 1 = Homebrew (Recommended), Option 2 = Download DMG, Option 3 = Build from Source, Option 4 = CLI Commands
• Nightly section: added brew install --cask vocamac-nightly as the recommended method
• Requirements: updated DMG-specific language to be method-agnostic

Website (web/)

• Hero section: added "Quick Install" button that, when clicked, reveals a mini terminal with brew tap jatinkrmalik/vocamac && brew install --cask vocamac and a copy button
• Install section: three tabs now — 🍺 Homebrew (default/active), 📦 Download DMG, 🛠️ Build from Source
• Install tab JS: updated switchInstallTab to handle three tabs, added toggleQuickInstall and copyQuickInstall functions
• FAQ: "How do I update?" now mentions both Homebrew and DMG paths
• CSS: added .hero__quick-install and .hero__quick-install-hint styles
• Feature pages: updated github-release-updates.md to mention Homebrew update flow; updated smart-model-selection.md to remove DMG-specific language

Docs

• ARCHITECTURE.md: distribution strategy reordered (Homebrew feat: VocaMac MVP — Local Voice-to-Text for macOS #1, GitHub Releases feat: Add install script for easy setup #2); UpdateChecker section documents both DMG and Homebrew update flows
• HOMEBREW.md: added "recommended" banner at top; updated overview language

Files Changed

File	Changes
README.md	+29/-6
web/layouts/index.html	+125/-14
web/static/style.css	+13
web/content/features/github-release-updates.md	+8/-4
web/content/features/smart-model-selection.md	+1/-1
docs/ARCHITECTURE.md	+18/-3
docs/HOMEBREW.md	+4/-3

No Swift source code changes — the in-app Homebrew detection and update flow (PR #159) already handles this correctly.