feat: add Microsoft Foundry provider support (#684)

* feat: add Azure AI Foundry provider support

Add support for Azure AI Foundry as a fourth cloud provider option alongside Anthropic API, AWS Bedrock, and Google Vertex AI.

Changes:
- Add use_foundry input to enable Azure AI Foundry authentication
- Add Azure environment variables (ANTHROPIC_FOUNDRY_RESOURCE, ANTHROPIC_FOUNDRY_API_KEY, ANTHROPIC_FOUNDRY_BASE_URL)
- Support automatic base URL construction from resource name
- Add validation logic with mutual exclusivity checks for all providers
- Add comprehensive test coverage (7 Azure-specific tests, 3 mutual exclusivity tests)
- Add complete Azure AI Foundry documentation with OIDC and API key authentication
- Update README to reference Azure AI Foundry support

Features:
- Primary authentication via Microsoft Entra ID (OIDC) using azure/login action
- Optional API key authentication fallback
- Custom model deployment name support via ANTHROPIC_DEFAULT_*_MODEL variables
- Clear validation error messages for missing configuration

All tests pass (25 validation tests total).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

* refactor: rename Azure AI Foundry to Microsoft Foundry and remove API key support

- Rename all references from "Azure AI Foundry" to "Microsoft Foundry"
- Remove ANTHROPIC_FOUNDRY_API_KEY support (OIDC only)
- Update documentation to reflect OIDC-only authentication
- Update tests to remove API key test case

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

* docs: simplify Microsoft Foundry setup and remove URL auto-construction

- Link to official docs instead of duplicating setup instructions
- Remove automatic base URL construction from resource name
- Pass ANTHROPIC_FOUNDRY_BASE_URL as-is

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

---------

Co-authored-by: Claude <noreply@anthropic.com>

action.yml

@@ -44,7 +44,7 @@ inputs:
 
   # Auth configuration
   anthropic_api_key:
-    description: "Anthropic API key (required for direct API, not needed for Bedrock/Vertex)"
+    description: "Anthropic API key (required for direct API, not needed for Bedrock/Vertex/Foundry)"
     required: false
   claude_code_oauth_token:
     description: "Claude Code OAuth token (alternative to anthropic_api_key)"
@@ -60,6 +60,10 @@ inputs:
     description: "Use Google Vertex AI with OIDC authentication instead of direct Anthropic API"
     required: false
     default: "false"
+  use_foundry:
+    description: "Use Microsoft Foundry with OIDC authentication instead of direct Anthropic API"
+    required: false
+    default: "false"
 
   claude_args:
     description: "Additional arguments to pass directly to Claude CLI"
@@ -244,6 +248,7 @@ runs:
         ANTHROPIC_CUSTOM_HEADERS: ${{ env.ANTHROPIC_CUSTOM_HEADERS }}
         CLAUDE_CODE_USE_BEDROCK: ${{ inputs.use_bedrock == 'true' && '1' || '' }}
         CLAUDE_CODE_USE_VERTEX: ${{ inputs.use_vertex == 'true' && '1' || '' }}
+        CLAUDE_CODE_USE_FOUNDRY: ${{ inputs.use_foundry == 'true' && '1' || '' }}
 
         # AWS configuration
         AWS_REGION: ${{ env.AWS_REGION }}
@@ -264,6 +269,13 @@ runs:
         VERTEX_REGION_CLAUDE_3_5_SONNET: ${{ env.VERTEX_REGION_CLAUDE_3_5_SONNET }}
         VERTEX_REGION_CLAUDE_3_7_SONNET: ${{ env.VERTEX_REGION_CLAUDE_3_7_SONNET }}
 
+        # Microsoft Foundry configuration
+        ANTHROPIC_FOUNDRY_RESOURCE: ${{ env.ANTHROPIC_FOUNDRY_RESOURCE }}
+        ANTHROPIC_FOUNDRY_BASE_URL: ${{ env.ANTHROPIC_FOUNDRY_BASE_URL }}
+        ANTHROPIC_DEFAULT_SONNET_MODEL: ${{ env.ANTHROPIC_DEFAULT_SONNET_MODEL }}
+        ANTHROPIC_DEFAULT_HAIKU_MODEL: ${{ env.ANTHROPIC_DEFAULT_HAIKU_MODEL }}
+        ANTHROPIC_DEFAULT_OPUS_MODEL: ${{ env.ANTHROPIC_DEFAULT_OPUS_MODEL }}
+
     - name: Update comment with job link
       if: steps.prepare.outputs.contains_trigger == 'true' && steps.prepare.outputs.claude_comment_id && always()
       shell: bash