fix(schema): replace anyOf unions with flat params for Gemini compatibility

[firecrawl-spring]

Summary

Google Gemini's function calling API rejects the MCP server's tool schemas because anyOf is used alongside other fields in the formats and parsers parameters. Gemini requires that when anyOf is present in a schema node, it must be the only property — no sibling fields are allowed.

This PR removes all z.union() (which produces anyOf in JSON Schema) from the tool definitions and replaces them with flat parameter alternatives that are compatible with all LLM providers.

Changes

• formats: Changed from z.union([enum, object, object]) to a simple z.enum() array. Added 'json' to the enum values.
• jsonOptions: New optional param for JSON extraction prompt and schema (used when 'json' is in formats).
• screenshotOptions: New optional param for screenshot fullPage, quality, and viewport (used when 'screenshot' is in formats).
• parsers: Changed from z.union([enum, object]) to a simple z.enum(['pdf']) array.
• pdfOptions: New optional param for maxPages (used when 'pdf' is in parsers).
• webhook (crawl tool): Changed from z.union([string, object]) to a simple z.string(), with a new webhookHeaders param.
• Added helper functions (buildFormatsArray, buildParsersArray, buildWebhook, transformScrapeParams) that reassemble the nested format the Firecrawl API expects from the flat MCP params at execution time.
• Updated tool description examples to use the new flat param style.

How it works

The MCP schema now uses simple, flat parameters that all LLM function-calling implementations can handle. At execution time, helper functions transform these flat params back into the nested format the Firecrawl API expects. This is transparent to both the LLM and the API.

Before (breaks Gemini):

{ "formats": [{ "type": "json", "prompt": "Extract data", "schema": {...} }] }

After (works everywhere):

{ "formats": ["json"], "jsonOptions": { "prompt": "Extract data", "schema": {...} } }

Testing

• Build passes (npm run build)
• No remaining z.union() calls in source
• Backward compatible: simple format usage like ["markdown"] works unchanged

Closes #164

[Chadha93]

I've verified this fix locally