docs: restructure integrations section

[marcel-rbro]

Restructures `sources/platform/integrations/` into four top-level folders and applies Lukas Bekr's 2026-05-03 tier list as `sidebar_position` (1 = S, 2 = Mid, 3 = Other). URLs are unchanged - slugs stay flat. Closes #2505.

Supersedes #2506 (built off master, fewer folders, no `index.mdx` rewrite).

Folder structure

Folder	Contents
`built-in/`	API, Actors, Webhooks, MCP (with ChatGPT and Claude Desktop subpages), GitHub
`ai/`	AI SDKs/frameworks, AI assistants (incl. Gumloop, ActivePieces), MCP-adjacent payments (x402, Skyfire), vector DBs
`workflow-automation/`	Make, n8n, Zapier, IFTTT, Workato, Windmill, Kestra, Pipedream, viaSocket, Bubble, Dify, plus comms destinations (Slack, Gmail, Telegram)
`data-storage/`	Airtable, Snowflake, Keboola, Airbyte, Drive

Tiers applied

• S-tier (1): all built-ins (API, Actors, Webhooks, MCP), n8n, Make, Zapier, OpenClaw, Gumloop, Google ADK, LangChain, OpenAI Agents SDK, Vercel AI SDK, Airtable, Snowflake, Manus, x402, Pinecone, GitHub
• Mid (2): Dify, Workato, Windmill, Bubble, IFTTT, Lindy, Amazon Bedrock, CrewAI, Keboola, Gmail, Telegram, Slack, Upsonic
• Other (3): Agno, Flowise, Haystack, Langflow, LangGraph, LlamaIndex, Mastra, Milvus, OpenAI Assistants, Qdrant, Skyfire, ActivePieces, Kestra, Pipedream, viaSocket, Airbyte, Drive
• Pending (no sidebar_position): Strands Agents, Agent onboarding guide - awaiting Lukas's input

Out of scope (will follow in a separate PR)

• `index.mdx` rewrite to reflect the new groupings and tier ordering
• New pages for empty landing page categories (Coding agents and IDEs, App builders, etc.)

Open questions for Lukas

1. Tier for the pending integrations - Strands Agents and the agent-onboarding guide. Default is Other; should either be promoted?
2. Tier for older still-open PRs that predate the list - Albato (docs: add Albato integration page #2481), Camunda (docs: add docs for Camunda integration #2159), Microsoft Power Automate (docs: add docs for Microsoft Power Automate integration #2101), Scalekit (docs: add Scalekit integration page #2570), Softr (docs: add Softr integration page #2573). Default Other on merge, OK?
3. Should Gumloop stay in `ai/` (as an AI assistant) or move back to `workflow-automation/`? The landing page lists it under workflow automation but its docs frame it as an AI agent platform.
4. GitHub placed under `built-in/`. Confirm this is correct - it sits between built-in and developer-tools.

Verification

• `pnpm build` passes locally (broken-link check via `onBrokenLinks: 'throw'`).
• All slugs preserved; no URL changes.

[apify-service-account]

✅ Preview for this PR (commit f2024ad) is ready at https://pr-2610.preview.docs.apify.com (see action run).