refactor(js): centralize server/browser category predicates

[mydea]

DESCRIBE YOUR PR

Stacked PR. Part of the JavaScript guide-categories series (#19492 → #19506). Depends on #19494; review/merge bottom-up.

Extract the repeated categories.includes('server') || includes('serverless') logic into shared hasServerCategory / hasBrowserCategory helpers (src/categories.ts) and use them in sdkOption and platformLink.

• Behavior-preserving cleanup; no rendered output changes.
• The nextjs/sveltekit env-var exclusion in shouldShowEnvVar is intentionally left as a framework-specific special case.

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• Checked Vercel preview for correctness, including links
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Project	Deployment	Actions	Updated
develop-docs	Ready	Preview	Sep 21, 2026 8:14am UTC
sentry-docs	Ready	Preview	Sep 21, 2026 8:14am UTC

[sentry]

Bug: The hasServerCategory and hasBrowserCategory helpers fail to check for the 'server-only' and 'browser-only' categories, respectively, making them logically incomplete.
_{Severity: LOW}

Suggested Fix

Update the helper functions to include checks for the '-only' category variants. The hasServerCategory function should be modified to also return true if the categories include 'server-only', and hasBrowserCategory should be updated to include 'browser-only'.

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: src/categories.ts#L10-L12

Potential issue: The new helper functions `hasServerCategory` and `hasBrowserCategory`
do not correctly handle all possible category types. Specifically, `hasServerCategory`
checks for `'server'` and `'serverless'` but omits the `'server-only'` category.
Similarly, `hasBrowserCategory` checks for `'browser'` but omits `'browser-only'`. While
these `'-only'` categories are defined in the `PlatformCategory` type, they are not
currently used in the codebase. This means the bug is latent and would only be triggered
if a developer creates a new platform using these categories, which could lead to
incorrect UI rendering or logic.

Also affects:

• src/categories.ts:18~20

_{Did we get this right? 👍 / 👎 to inform future reviews.}