feat(skills-next): add cocoa SDK references

[evanpurkhiser]

Direct LLM port of the existing cocoa SDK skill into the skills-next per-SDK reference layout under skills-next/references/sdks/cocoa/. This content has NOT been reviewed at all — it is a machine-generated port of the existing SDK skill, and every file should be treated as unverified.

[evanpurkhiser]

Automated fixes pushed addressing the review feedback on this PR:

• tracing.md: fixed the tracePropagationTargets example. A raw String was used for a regex pattern, which the Cocoa SDK treats as a substring match; the regex is now wrapped in NSRegularExpression(pattern:) and the array typed as [Any], matching the documented API (strings match as substrings, regexes require NSRegularExpression).

Unreviewed LLM-port correction; please verify against the SDK.

[sentry]

Bug: The cross-linking table in the Cocoa SDK documentation contains relative markdown links that point to non-existent files, such as ../go/index.md.
_{Severity: HIGH}

Suggested Fix

Correct the broken relative links. Either create the missing documentation files (e.g., go/index.md, python/index.md) at the specified paths or revert the links to the plain text identifiers used previously, like sentry-go-sdk. Creating the files would be a more robust long-term solution.

Prompt for AI Agent

Review the code at the location below. A potential bug has been identified by an AI
agent. Verify if this is a real issue. If it is, propose a fix; if not, explain why it's
not valid.

Location: skills-next/references/sdks/cocoa/index.md#L419-L424

Potential issue: The pull request updated a table in the Cocoa SDK documentation,
changing plain text skill identifiers like `sentry-go-sdk` to relative markdown links
such as `[`go`](../go/index.md)`. However, the target files for these links (e.g.,
`skills-next/references/sdks/go/index.md`) do not exist in the repository. The
documentation's instructions expect an automated agent to load these reference files. An
agent attempting to follow these links to set up distributed tracing with a backend
service will encounter file-not-found errors, breaking the setup workflow.