Rebuild the landing hero around the interactive example

[SaladDay]

Rebuilds the landing hero around the interactive example (docs polish audit-readme-landing findings 1, 4, 5, 7, 8, 13, 14, 15, 19).

• Hero (option A): ComposeLab moves into the hero. The launch video is a "Watch the launch film" link that opens the modal and loads the video only on click. Eyebrow, HUD, ticker, ASCII logo and ASCII outro are deleted, as are the section numbers, kickers, ledes, captions and meta rows (no text under 14 px, measured in the browser at 1440 and 390 px).
• Facts: the prerequisites line is gone; the install box has macOS / Linux and Windows tabs. CTAs: "Get started" goes to Install Core and Web; the outro links Install Core and Web, Add and manage nodes and Run your first Session. Link labels equal page titles; hedging copy and slogan repeats are rewritten.
• The tagline: the hero lede and the description in config.mts (EN and zh) use the unified sentence; the description frontmatter in index.md and zh/index.md is removed. Footer copyright is "Copyright © 2026-present MiniMax-AI".
• Phone SessionFlow scales to the column width instead of scrolling an empty box; Harness icons and the logo wall are visible in the light theme (brands unchanged). The architecture figure uses architecture-dark.svg in the dark theme. Space Grotesk loads from the landing only.
• Dead code: TypeTerminal.vue, AsciiCanvas.vue, about 30 unused Landing.vue selectors and unrendered copy fields; SessionFlow copy moves into landing-content.ts. docs.data.mts is left to lane N.

Checks: pnpm --dir website build && pnpm --dir website test pass (24 tests). Screenshots (EN/zh, 1440/390, dark/light, stepped scroll): http://10.13.94.7:9999/landing-l/. Skipped: make check-docs and translations tests (no docs changes).

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