docs(readme): drop SDK v1 mentions, migrate to app.aixplain.com, refresh Agentic OS diagram

[nurhamdan1987]

What changed

• Dropped all SDK v1 mentions — removed both v1 deprecation callouts (Quick start header and the legacy note after the team-agent example). The README now documents the SDK (v2) as simply "the SDK".
• Domain migration — studio.aixplain.com/browse → app.aixplain.com/marketplace (studio/console deprecated 2026-08-24; canonical domain is app.aixplain.com). Marketplace badge and link both updated.
• Renamed docs page — "MCP servers docs" link → /api-reference/marketplace (the page was renamed to Marketplace).
• Dropped "edge" from the deployment prose → cloud, on-prem, and local (keeps "local" as the mode; "Desktop" is the local app). Applied to the intro, "Why aixplain", "How it works", the diagram alt text, and "Data handling and deployment".
• Refreshed the Agentic OS diagram — synced the revised SVG: Planner + Orchestrator merged into one box, Evolver annotation removed, Deployment Engine removed, Workspace Engine → Workspaces, Agent Engine → Agent Runtime, Edge deploy pill dropped, ampersands → "and".

Kept the 900+ models, tools, and integrations count as-is (that's the models/tools/integrations slice, distinct from the total-assets figure).

🤖 Generated with Claude Code