The gnostic OpenAPI generator hardcodes `format: enum`, `format: bytes`,
and `format: field-mask` on string properties. These are OpenAPI-only
markers; MCP clients treat tool schemas as JSON Schema 2020-12 and warn
or fail on them (zod-based parsers log "unknown format" for every tool
on every load, ajv strict mode rejects the definitions).
Normalize schemas as they leave the resolver and when parameter schemas
are cloned: drop `format: enum` (the `enum` keyword is already present),
rewrite `format: bytes` to `contentEncoding: base64`, and drop
`format: field-mask`. The generated openapi.yaml is unchanged.
A catalog test now walks every curated tool's input and output schema
and fails on any format outside the registered allowlist.
Fixes#6262
