feat(landing): rewrite around local-first proposition + architecture diagram

Reframe the landing page around what makes Scrum4Me unique: code execution
stays on the developer's own hardware (laptop, NAS or VM). The Vercel UI and
Neon DB are a metadata coordination layer; source code never leaves the local
worker. Adds a mermaid-rendered architecture diagram (two-zone: Scrum4Me-stack
vs Jouw kant) with light/dark variants generated via mmdc.

Page changes (app/page.tsx):
- Hero: H1 "Plannen in de cloud. Uitvoeren op je eigen machine." + new
  subhead; CTA "Hoe het werkt" replaces "Demo bekijken" (anchors to
  #architectuur).
- New section §3 "Architectuur" with light/dark SVG and 4 callout-cards
  (Vercel · Neon · Lokale worker · GitHub) honestly describing what each
  component stores or runs.
- Feature grid: 6 cards (set C) — combines Sprint Board + Solo Paneel,
  adds Lokale Claude-agents, Realtime updates, Async vraagkanaal, Todo's.
  LIVE callout removed (folded into Realtime card).
- "Twee manieren"-section replaced by a Quickstart with concrete git-clone
  snippet for the MCP-server.
- Handleiding: 9 → 10 steps; MCP recommended in step 8; new step 9
  "Story laten uitvoeren" describing the Voer-uit / job-queue flow;
  step 1 mentions QR-pairing as alternative login.
- Footer: adds link to madhura68/scrum4me-mcp alongside the app repo.

Tooling:
- New docs/diagrams/architecture.mmd (mermaid source).
- New npm script "diagrams" generates light + dark SVG via mmdc; output
  committed to public/diagrams/. No prebuild hook (manual regenerate, like
  prisma generate / docs:index).
- Plan + grilling outcomes captured in docs/plans/landing-local-first.md.

Tracked under Scrum4Me story cmoq2qoik0001qa175iynfnaa
(PBI Marketing & Landingspagina, cmoq2q50s0000qa174rmrjove).

Verified: npm run lint (0 new errors), npm test (379/379), npm run build OK.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs/INDEX.md

@@ -34,6 +34,7 @@ Auto-generated on 2026-05-03 from front-matter and headings.
 |---|---|---|
 | [Docs-restructuur — geoptimaliseerd voor AI-lookup](./plans/docs-restructure-ai-lookup.md) | proposal | 2026-05-02 |
 | [PBI Bulk-Create Spec — Docs-Restructure for AI-Optimized Lookup](./plans/docs-restructure-pbi-spec.md) | done | 2026-05-03 |
+| [Landing v2 — lokaal & veilig + architectuurdiagram](./plans/landing-local-first.md) | active | 2026-05-03 |
 | [M10 — Password-loze inlog via QR-pairing](./plans/M10-qr-pairing-login.md) | active | 2026-05-03 |
 | [M11 — Claude vraagt, gebruiker antwoordt](./plans/M11-claude-questions.md) | active | 2026-05-03 |
 | [M9 — Actief Product Backlog](./plans/M9-active-product-backlog.md) | active | 2026-05-03 |