Alpha front door: rewrite README top as a 20-second wedge landing (EN + RU)

[PhysShell]

Agent brief — tier: basic. One PR for this issue only (Closes #<this>); branch from main. House rules: AGENTS.md.

Goal

README.md still opens as "# OwnLang — PoC" — deep, research-framed, no wedge landing. Rewrite the top of README.md (and mirror it in README.ru.md) into a 20-second landing: a newcomer should know within 20 seconds what to install and what it finds. Per docs/notes/alpha-readiness.md this is the highest-leverage missing piece of the alpha.

Sources of truth (read first, do not invent)

• docs/notes/alpha-readiness.md — the wedge, the recorded slogans, the A–G gate.
• docs/ROADMAP.md — the one-sentence pitch and the "Positioning against the competition" section.
• action.yml — Action inputs for the quickstart snippet.
• scripts/own-check.sh — the current CLI surface.

Deliverable (top of README, both languages)

1. The one-sentence pitch, verbatim from ROADMAP ("Own.NET finds lifetime/resource bugs that C# cannot express: WPF/event leaks, missing Dispose, DI lifetime mismatch, pooled-buffer misuse").
2. Copy-paste quickstart: the ~6-line GitHub Action YAML + the scripts/own-check.sh invocation.
3. One bad → diagnostic example (take one from examples/gallery/).
4. A short "why not Sonar/CodeQL/Semgrep" paragraph linking the ROADMAP positioning section.
5. Placeholder sections "Case studies" and "Suppression & false positives" — follow-up PRs from the sibling issues only add single-line links there (this avoids README merge conflicts; this issue owns the README structure).
6. Existing research content is moved below / behind links, not deleted.

Guardrails

• Never pitch as "static analyzer / SAST / AI code reviewer / borrow checker for C#" — the refusal is on record in alpha-readiness.md.
• Use the recorded slogans; do not coin new ones.
• Doc-only change; still run ruff check . before committing.

Done when

A newcomer reading only the first screen knows: what it is, the install/run snippet, one concrete bug it catches, and where the deeper docs live.