Add --no-open and --local-schema CLI flag documentation

[mintlify]

Summary

• Added documentation for --no-open flag in mint dev command to prevent browser from opening automatically
• Added documentation for --local-schema flag in mint openapi-check command for checking locally hosted OpenAPI files over HTTP

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Note

Low Risk
Low risk documentation-only change adding examples for two existing CLI flags; no product code or runtime behavior is modified.

Overview
Updates installation.mdx to document two CLI options: mint dev --no-open to prevent auto-opening the browser, and mint openapi-check --local-schema to validate an OpenAPI spec served over local HTTP (with a note that HTTPS-only applies in production).

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