feat: refocus the landing pages on the key selling points

[everpcpc]

Goal

Refocus the three landing pages (home, reader, server) on their key selling points. The home page duplicated most of the reader page, and big cards were spent on minor items (heap profiling, LTR/RTL, page modes) while flagship features were buried in body text.

Changes

• Home (/): 12 sections → 8. Dropped the four sections that duplicate /reader/ (Reading, Offline, Apple platforms, Apple integration); the page now tells the ecosystem story: hero → "Already using Komga?" → KMReader pitch → KMServer pitch → demo → ecosystem diagram → open source → CTA. Hero sub names both products; the KMReader pitch names DIVINA, offline downloads and progress sync.
• Reader (/reader/): Reading section 6 cards → 4 (DIVINA, Webtoon, EPUB, PDF) in the 4-column grid; LTR/RTL and page modes folded into card bodies instead of their own cards. New "Bring your own server." section stating Komga 1.20.0+ compatibility and linking to /server/.
• Server (/server/): "Beyond compatibility" cards are now CJK cross-search, Smart lists and Reading stats; heap profiling dropped (stays documented in Development) and Natural sort demoted to a chip. "Why KMServer?" 4 cards → 3: "Written in Rust" and "Runs anywhere" merged into "One static binary".

Test

• pnpm typecheck && pnpm build && pnpm exec nimbus-docs check && pnpm lint:docs all green.
• Verified every public route from AGENTS.md still exists in dist/.