docs(site): polish copy, logo emoji, and link formatting

[seanseannery]

Key Changes

• Update header logo to >_ 🚨 Opsfile (terminal symbol + rotating light emoji)
• Update subtitle: "Create an Opsfile. Run `ops prod rollback-cluster`. Go back to sleep."
• Shorten Team Standardisation card: "No more tribal knowledge or bespoke bash aliases. Opsfile lives in the repo."
• Shorten Secrets-Safe card: "Reference secrets via environment variables — never commit them."
• Add : after each bold header in the Links section
• Replace copy button text with 📋/✅ emoji; title and aria-label retain "Copy" for accessibility
• Style inline `code` in subtitle to match tagline (cyan monospace on dark bg)

Why do we need this?

Polish pass on the GitHub Pages landing page — tightening copy, improving visual identity with a recognisable logo treatment, and making the copy button less visually noisy.

New modules or other dependencies introduced

None

How was this tested?

Visually reviewed in browser. Copy button interaction verified (📋 → ✅ → 📋 after 2s). Pages deploy will confirm rendering at seanseannery.github.io/opsfile on merge.