refactor: restructure documentation into organized docs directory (anthropics#383)

- Move FAQ.md to docs/faq.md
- Create structured documentation files:
  - setup.md: Manual setup and custom GitHub app instructions
  - usage.md: Basic usage and workflow configuration
  - custom-automations.md: Automation examples
  - configuration.md: MCP servers and advanced settings
  - experimental.md: Execution modes and network restrictions
  - cloud-providers.md: AWS Bedrock and Google Vertex setup
  - capabilities-and-limitations.md: Features and constraints
  - security.md: Security information
- Condense README.md to overview with links to detailed docs
- Keep CONTRIBUTING.md, SECURITY.md, CODE_OF_CONDUCT.md at top level

Author: ashwin-ant

README.md

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+# Capabilities and Limitations
+
+## What Claude Can Do
+
+- **Respond in a Single Comment**: Claude operates by updating a single initial comment with progress and results
+- **Answer Questions**: Analyze code and provide explanations
+- **Implement Code Changes**: Make simple to moderate code changes based on requests
+- **Prepare Pull Requests**: Creates commits on a branch and links back to a prefilled PR creation page
+- **Perform Code Reviews**: Analyze PR changes and provide detailed feedback
+- **Smart Branch Handling**:
+  - When triggered on an **issue**: Always creates a new branch for the work
+  - When triggered on an **open PR**: Always pushes directly to the existing PR branch
+  - When triggered on a **closed PR**: Creates a new branch since the original is no longer active
+- **View GitHub Actions Results**: Can access workflow runs, job logs, and test results on the PR where it's tagged when `actions: read` permission is configured (see [Additional Permissions for CI/CD Integration](./configuration.md#additional-permissions-for-cicd-integration))
+
+## What Claude Cannot Do
+
+- **Submit PR Reviews**: Claude cannot submit formal GitHub PR reviews
+- **Approve PRs**: For security reasons, Claude cannot approve pull requests
+- **Post Multiple Comments**: Claude only acts by updating its initial comment
+- **Execute Commands Outside Its Context**: Claude only has access to the repository and PR/issue context it's triggered in
+- **Run Arbitrary Bash Commands**: By default, Claude cannot execute Bash commands unless explicitly allowed using the `allowed_tools` configuration
+- **Perform Branch Operations**: Cannot merge branches, rebase, or perform other git operations beyond pushing commits
+
+## How It Works
+
+1. **Trigger Detection**: Listens for comments containing the trigger phrase (default: `@claude`) or issue assignment to a specific user
+2. **Context Gathering**: Analyzes the PR/issue, comments, code changes
+3. **Smart Responses**: Either answers questions or implements changes
+4. **Branch Management**: Creates new PRs for human authors, pushes directly for Claude's own PRs
+5. **Communication**: Posts updates at every step to keep you informed
+
+This action is built on top of [`anthropics/claude-code-base-action`](https://github.com/anthropics/claude-code-base-action).

docs/capabilities-and-limitations.md

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+# Cloud Providers
+
+You can authenticate with Claude using any of these three methods:
+
+1. Direct Anthropic API (default)
+2. Amazon Bedrock with OIDC authentication
+3. Google Vertex AI with OIDC authentication
+
+For detailed setup instructions for AWS Bedrock and Google Vertex AI, see the [official documentation](https://docs.anthropic.com/en/docs/claude-code/github-actions#using-with-aws-bedrock-%26-google-vertex-ai).
+
+**Note**:
+
+- Bedrock and Vertex use OIDC authentication exclusively
+- AWS Bedrock automatically uses cross-region inference profiles for certain models
+- For cross-region inference profile models, you need to request and be granted access to the Claude models in all regions that the inference profile uses
+
+## Model Configuration
+
+Use provider-specific model names based on your chosen provider:
+
+```yaml
+# For direct Anthropic API (default)
+- uses: anthropics/claude-code-action@beta
+  with:
+    anthropic_api_key: ${{ secrets.ANTHROPIC_API_KEY }}
+    # ... other inputs
+
+# For Amazon Bedrock with OIDC
+- uses: anthropics/claude-code-action@beta
+  with:
+    model: "anthropic.claude-3-7-sonnet-20250219-beta:0" # Cross-region inference
+    use_bedrock: "true"
+    # ... other inputs
+
+# For Google Vertex AI with OIDC
+- uses: anthropics/claude-code-action@beta
+  with:
+    model: "claude-3-7-sonnet@20250219"
+    use_vertex: "true"
+    # ... other inputs
+```
+
+## OIDC Authentication for Bedrock and Vertex
+
+Both AWS Bedrock and GCP Vertex AI require OIDC authentication.
+
+```yaml
+# For AWS Bedrock with OIDC
+- name: Configure AWS Credentials (OIDC)
+  uses: aws-actions/configure-aws-credentials@v4
+  with:
+    role-to-assume: ${{ secrets.AWS_ROLE_TO_ASSUME }}
+    aws-region: us-west-2
+
+- name: Generate GitHub App token
+  id: app-token
+  uses: actions/create-github-app-token@v2
+  with:
+    app-id: ${{ secrets.APP_ID }}
+    private-key: ${{ secrets.APP_PRIVATE_KEY }}
+
+- uses: anthropics/claude-code-action@beta
+  with:
+    model: "anthropic.claude-3-7-sonnet-20250219-beta:0"
+    use_bedrock: "true"
+    # ... other inputs
+
+  permissions:
+    id-token: write # Required for OIDC
+```
+
+```yaml
+# For GCP Vertex AI with OIDC
+- name: Authenticate to Google Cloud
+  uses: google-github-actions/auth@v2
+  with:
+    workload_identity_provider: ${{ secrets.GCP_WORKLOAD_IDENTITY_PROVIDER }}
+    service_account: ${{ secrets.GCP_SERVICE_ACCOUNT }}
+
+- name: Generate GitHub App token
+  id: app-token
+  uses: actions/create-github-app-token@v2
+  with:
+    app-id: ${{ secrets.APP_ID }}
+    private-key: ${{ secrets.APP_PRIVATE_KEY }}
+
+- uses: anthropics/claude-code-action@beta
+  with:
+    model: "claude-3-7-sonnet@20250219"
+    use_vertex: "true"
+    # ... other inputs
+
+  permissions:
+    id-token: write # Required for OIDC
+```