Add an AWS deployment planning skill for Prebid Server Go

[ChristianPavilonis]

Summary

• Add an explicitly invoked skill for planning Prebid Server Go deployments on AWS and generating approved Terraform and runtime files.
• Gather workload, availability, scaling, security, and budget requirements before choosing services, rather than treating one pilot architecture as the default.
• Keep file generation separate from cloud execution, with HashiCorp references and safeguards for secrets, Terraform tests, state migration, and deployment approvals.

Changes

All files are under .claude/skills/planning-prebid-aws/.

File	Change
SKILL.md	Defines the requirements interview, design approval, file-generation workflow, and explicit invocation setting.
references/architecture.md	Connects AWS service choices to workload, availability, networking, and cost requirements.
references/prebid-go.md	Covers bidder access, caller integration, privacy, stored requests, cache, and pilot rollback requirements.
references/terraform.md	Adds versioned HashiCorp skill references, backend and authentication rules, safe local testing, and protected plan review.
references/file-generation.md	Defines ownership and validation for runtime files, deployment tools, secrets handling, and runbooks.
examples/two-region-pilot.md	Provides a conditional pilot example and walkthrough cases for production scaling, cache dependencies, unsafe tests, and backend migration.

Scope

Six Markdown files for one skill. The main workflow stays short, with detailed guidance in focused references. This PR adds instructions for producing deployment files, not a deployed environment or a fixed Terraform template. It changes no application code, infrastructure, credentials, traffic, or skill installation settings.

Closes

Closes #1163

Test plan

• Scoped formatting: npx --yes prettier@3.4.2 --check --config docs/.prettierrc '.claude/skills/planning-prebid-aws/**/*.md'.
• Python structural check: six Markdown files, valid required frontmatter constraints, explicit invocation enabled, seven local links and anchors, balanced code fences, and whitespace.
• git diff --cached --check and final staged diff review.
• Manual document walkthrough for pilot/production choices and authorization boundaries, including mixed real/mocked Terraform providers and existing DynamoDB locking.
• Fresh-agent invocation and end-to-end file-generation exercise.

Rust, JavaScript, WASM, and documentation-site checks were not run because their code and inputs are unchanged. The scoped formatting command covers these skill files outside docs/. Terraform is not installed locally; no Terraform configuration was generated or executed, and no AWS actions were performed.

Checklist

• Changes follow repository conventions.
• No secrets or credentials committed.
• Skill requires explicit invocation with disable-model-invocation: true.
• Runtime-code assertions and logging checks are not applicable to this documentation-only change.
• Fresh-agent behavior verified before marking ready for review.