docs: move platform security reference into Contributing docs

[spydon]

What

Moves the root SECURITY.md to docs/contributing/security.md and adds it to the MkDocs nav under Contributing → Security Internals.

References supabase/.github#20

Why

The root SECURITY.md is not a vulnerability-disclosure policy. It's contributor/implementation documentation (WASM checksum verification, credential masking, response size limits) that cites source files like wasm_fdw.rs and utils.rs and shows how to use internal utilities such as sanitize_error_message.

Because GitHub treats any root SECURITY.md as the repo's "Security policy", this file was overriding the organization-wide disclosure policy maintained in supabase/.github. Moving it:

• keeps the implementation reference on the docs site, next to the other Contributing pages, and
• frees the Security-policy slot so this repo inherits the org-wide default.

The existing user-facing docs/guides/security.md (FDW usage, RLS, security definer) is unaffected; this is a separate, contributor-focused document.

Note

Takes effect alongside supabase/.github#20.

[Copilot]

Pull request overview

This PR relocates the platform “security internals” documentation out of the repository root (where GitHub interprets SECURITY.md as a disclosure policy) and into the Contributing documentation section, so the repo can inherit the organization-wide security policy while still keeping contributor-focused implementation notes.

Changes:

• Adds a new Contributing doc page: docs/contributing/security.md (Wrappers platform security internals).
• Registers the new page in the MkDocs navigation under Contributing → Security Internals.

Reviewed changes

Copilot reviewed 1 out of 2 changed files in this pull request and generated no comments.

File	Description
mkdocs.yaml	Adds the new “Security Internals” page to the Contributing navigation.
docs/contributing/security.md	Introduces a contributor-focused security internals reference (WASM checksums, error sanitization, response limits, etc.).

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[burmecia]

thanks @spydon for flagging this!