docs: README reach — why-SysManager comparison table, one-line install CTA, star CTA

[laurentiu021]

Summary

Visibility/reach improvements to the README's first-impression surface (from the reach audit). docs: only, no release.

Changes

• One-line install CTA above the fold — winget command + direct portable .exe link right under the badges, so a visitor can install in the first screenful instead of scrolling to the Install section.
• Why SysManager? comparison table — honest, factual matrix vs CCleaner / Wintoys / O&O ShutUp10 / HWiNFO across open-source, no-telemetry, local, portable, and the feature surface. Drives the local-first/all-in-one positioning that converts visitors to stars. Footnoted that it reflects free editions as of 2026 and invites corrections.
• Star CTA + GitHub stars (social) badge — a friendly ask to star the repo (biggest lever for a solo OSS project's discoverability).

Notes

• Comparison is deliberately fair (⚠️ = partial/paywalled, not ❌) to stay credible.
• No feature claims invented — every SysManager ✅ maps to a real implemented tab.

Verification

• Markdown only; no code touched. Internal links unaffected.