feat(skills-next): add tanstack-start SDK references

[evanpurkhiser]

Direct LLM port of the existing tanstack-start SDK skill into the skills-next per-SDK reference layout under skills-next/references/sdks/tanstack-start/. 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 fix pushed addressing the review feedback on this PR:

• index.md: replaced the deprecated sendDefaultPii: true with the recommended dataCollection API in both the client and server config examples, and updated the Configuration Reference table (marked sendDefaultPii deprecated, added a dataCollection row). The ../<slug>/index.md cross-SDK links were left untouched (separate design decision).

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

[sentry]

Bug: The "Phase 4 Cross-Link" table contains broken relative links to other SDK guides, which point to non-existent files.
_{Severity: MEDIUM}

Suggested Fix

Update the relative links in the Phase 4 Cross-Link table to point to the correct, existing documentation paths. Alternatively, revert to the previous format of referencing the SDKs by name (e.g., `sentry-go-sdk`) instead of using file path links.

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/tanstack-start/index.md#L347-L352

Potential issue: The markdown file `skills-next/references/sdks/tanstack-start/index.md`
contains four broken relative links in the "Phase 4 Cross-Link" section. Links such as
`[go](../go/index.md)` point to non-existent files, as the corresponding `go/`,
`python/`, `ruby/`, and `node/` directories do not exist within the
`skills-next/references/sdks/` directory. This will cause 404 errors for users or
automated systems attempting to navigate to these linked SDK guides, preventing them
from accessing related documentation.

[sentry]

Bug: The documentation for dataCollection: {} omits a critical warning that passing an empty object enables permissive PII collection defaults, leading to unintentional data capture.
_{Severity: HIGH}

Suggested Fix

Update the documentation to restore the warning about the behavior of dataCollection. Specifically, explain that passing an empty object (e.g., {}) 'flips unset categories to their permissive defaults' and that users must explicitly opt-out of each category to disable them.

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/tanstack-start/index.md#L103-L108

Potential issue: The documentation recommends using `dataCollection: {}` but omits a
critical warning that was present in the original version. In the Sentry SDK, passing an
empty object to the `dataCollection` option enables permissive defaults for PII
collection, including `userInfo`, `cookies`, and `httpHeaders`. The new documentation
fails to mention this behavior, leading users who follow the code examples to
unknowingly enable broader data collection than intended. This constitutes a data
privacy regression.

Also affects:

• skills-next/references/sdks/tanstack-start/index.md:138~143
• skills-next/references/sdks/tanstack-start/index.md:262~262

[evanpurkhiser]

Merging these ahead of review to get the ball rolling on the new skills layout. @cleptric will follow up with SDK teams to finesse the content of the SDK references.