feat(mcp_modules): add csvjson community module (lossless CSV<->JSON, strict coercion, receipts)

[Larslllllll]

Adds a second community package for #2 (add more community packages): csvjson — lossless CSV ↔ JSON conversion for agents.

What it does

• Schema inference with widening (null < bool < int < float < str < json), like a spreadsheet import but explicit.
• Strict coercion: a value that cannot coerce raises SchemaError — "abc" in an int column fails loudly instead of becoming NaN or "".
• Nested objects/arrays flatten to dotted keys (meta.role, tags.0) and expand back losslessly.
• Union-of-columns protection (the hard part of heterogeneous CSV): blank cells in nested groups are ignored, container keys (tags) never receive scalars, scalar blanks stay real nulls, empty arrays round-trip via the [] marker.
• Reconciliation receipt on every conversion: rows/fields in→out, missing/added fields, changed cells, null counts, ok flag.

Endpoints

GET /csvjson · POST /csvjson/to-json · POST /csvjson/to-csv · POST /csvjson/schema · POST /csvjson/validate + /tools/csvjson/* tool endpoints with /*/info schemas, mirroring the webhook_verify module pattern.

Quality

• 28 mocha/chai tests, zero runtime dependencies, Node >= 20.10.
• Ported from the same core logic as the csvjson-kit product (36-test suite incl. test_heterogeneous.py, test_roundtrip.py): the union-of-columns and empty-array rules are the ones that passed regression testing there.
• README.md, docs/api.md, examples/basic-usage.js included.

cd mcp_modules/csvjson && npm install && npm test   # 28 passing