fix: only load GitHub MCP server when its tools are allowed (#124)

* fix: only load GitHub MCP server when its tools are allowed

- Add allowedTools parameter to prepareMcpConfig
- Check for mcp__github__ and mcp__github_file_ops__ tool prefixes
- Only include MCP servers when their tools are in allowed_tools
- Maintain backward compatibility when allowed_tools is not specified
- Update tests to reflect the new conditional loading behavior

This optimizes resource usage by not loading unnecessary MCP servers
when their tools are not allowed in the configuration.

Co-authored-by: ashwin-ant <ashwin-ant@users.noreply.github.com>

* fix: always load github_file_ops server regardless of allowed_tools

- Only apply conditional loading to the github MCP server
- Always load github_file_ops server as it contains essential tools
- Update tests to reflect this behavior

Co-authored-by: ashwin-ant <ashwin-ant@users.noreply.github.com>

* refactor: move allowedTools/disallowedTools parsing to parseGitHubContext

- Change allowedTools and disallowedTools from string to string[] in ParsedGitHubContext type
- Parse comma-separated environment variables into arrays in parseGitHubContext function
- Update create-prompt and install-mcp-server to use pre-parsed arrays
- Update all affected test files to use array syntax
- Eliminate duplicate parsing logic across the codebase

* style: apply prettier formatting

---------

Co-authored-by: claude[bot] <209825114+claude[bot]@users.noreply.github.com>
Co-authored-by: ashwin-ant <ashwin-ant@users.noreply.github.com>

test/prepare-context.test.ts

@@ -242,7 +242,7 @@ describe("parseEnvVarsWithContext", () => {
         ...mockPullRequestCommentContext,
         inputs: {
           ...mockPullRequestCommentContext.inputs,
-          allowedTools: "Tool1,Tool2",
+          allowedTools: ["Tool1", "Tool2"],
         },
       });
       const result = prepareContext(contextWithAllowedTools, "12345");