docs: rewrite AI Gateway for ADP GA release

[micheleRP]

Tracks: DOC-2109 — Configure your LLM provider (ADP Docs Plan Workflow #1)

Summary

• Replace the obsolete AI Gateway page set with a four-page structure (index + overview + configure-provider + connect-agent) matching the ai-agents/agents/ convention. Content is grounded in llm_provider.proto and the adp-ui form labels.
• Add page aliases so every old URL (what-is-ai-gateway, gateway-quickstart, admin/setup-guide, builders/connect-your-agent, cel-routing-cookbook, mcp-aggregation-guide, builders/discover-gateways, gateway-architecture) 301s to its natural successor.
• Flag every standalone-ADP detail (sign-in URL, IAM model, OIDC endpoints) with // TODO: pending live-environment verification — ADP is moving to its own product surface rather than nesting under Redpanda Cloud, and concrete URLs/IAM paths aren't finalized yet.

Context

Planning and scope: AI Gateway docs rewrite — ADP GA (2026-06-15) plan (Confluence). Parent workstream: ADP Docs Plan — Beta May 15 / GA June 15.

This is the first pass — the draft is ready for early review of structure and framing, but the // TODO: markers indicate content that needs verification against the live standalone ADP environment when it's available. More rounds of iteration to come before GA.

Preview pages

• AI Gateway (updated)
• AI Gateway Overview (new)
• Configure an LLM Provider (new)
• Connect Your Agent (new)

Test plan

• Netlify preview builds successfully
• AI Gateway section renders with four entries in nav (AI Gateway / Overview / Configure an LLM Provider / Connect Your Agent)
• Spot-check each of the eight redirect aliases resolves correctly on the preview
• Live-environment walkthrough for each of the five provider types (OpenAI, Anthropic, Google, Bedrock, OpenAI-compatible) once the standalone ADP UI is available — TODO markers identify the gaps
• Technical SME review for proto field accuracy (team-ai)
• Final docs-team-standards:review editorial pass before GA
• Remove the adp-la.adoc partial includes at GA (ADP ships as GA, not LA)

🤖 Generated with Claude Code

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[coderabbitai]

📝 Walkthrough

Walkthrough

This PR restructures the AI Gateway documentation by consolidating extensive multi-page guides into a simplified documentation set. Eight documentation pages covering setup workflows, architecture, CEL routing patterns, MCP aggregation, quickstart, discovery workflows, and conceptual overviews are removed, while three new pages focused on overviewing AI Gateway, configuring LLM providers, and connecting agents are introduced. The navigation structure is correspondingly simplified, and the index page description is updated to emphasize Redpanda as a managed LLM API proxy.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~15 minutes

Possibly related PRs

• DOC-2034: Document OIDC authentication for AI Gateway agent connections #516: Implements OIDC client_credentials authentication in connect-your-agent documentation, which aligns with the new connect-agent.adoc page that also features OIDC-based authentication patterns.
• Reorganize navigation structure and rename AI Agents to Agentic AI #490: Reorganizes AI Agents and MCP-related navigation entries in modules/ROOT/nav.adoc, addressing similar structural changes to the documentation sidebar.
• change admonition #507: Modifies the same set of AI Gateway documentation files (setup-guide, gateway pages), sharing overlap with content being removed and restructured.

Suggested reviewers

• birdayz
• paulohtb6
• weeco

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The pull request description does not follow the required template structure and is missing critical required fields.	Add the missing required sections from the description template: issue number link (Resolves #), Review deadline, and Page previews with proper formatting. Reformat to match the template structure.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title 'docs: rewrite AI Gateway for ADP GA release' clearly and concisely summarizes the main change—a documentation rewrite of AI Gateway aligned with the ADP GA release.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch adp-ai-gateway-rewrite

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