Polish repository presentation

[YKKULTRA]

What changed

• redesigned the README around SqueakyClean's evidence-first value proposition
• added a real dark-mode app screenshot, status badges, a scope table, an honest quick start, and a concise FAQ
• moved the detailed cleanup invariants and trust boundaries into Docs/SAFETY.md
• kept the current limits prominent: only dead user LaunchAgents are actionable, quarantine does not itself reclaim space, and public builds are not yet notarized

Why

The original README was technically thorough but read like internal engineering documentation. This makes the repository easier to understand at a glance without weakening or overstating the safety story.

User and developer impact

Visitors now get a clearer product overview, a real look at the UI, accurate build instructions, and a direct path to the full safety model. The app code and runtime behavior are unchanged.

Validation

• GitHub Markdown API rendered the README successfully
• all local README links resolve
• workflow and badge URLs return HTTP 200
• git diff --check passes
• screenshot verified as a 1312 x 884 PNG
• existing main CI is green