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>

package.json

@@ -18,7 +18,8 @@
     "seed": "prisma db seed",
     "docs:index": "node scripts/generate-docs-index.mjs",
     "docs:check-links": "node scripts/check-doc-links.mjs",
-    "docs": "npm run docs:index && npm run docs:check-links"
+    "docs": "npm run docs:index && npm run docs:check-links",
+    "diagrams": "mmdc -i docs/diagrams/architecture.mmd -t default -b transparent -o public/diagrams/architecture-light.svg && mmdc -i docs/diagrams/architecture.mmd -t dark -b transparent -o public/diagrams/architecture-dark.svg"
   },
   "dependencies": {
     "@base-ui/react": "^1.4.1",