docs(js): Review and update TanStack Start React quick start guide

[inventarSarah]

DESCRIBE YOUR PR

Reviewed the existing TanStack Start React quick start guide and made some updates:

• improved structures by adding subheadings
• rewrote some explanations to be more concise and in line with similar content in other QS guides
• updated verification code snippets (tested with the latest version of the framework)

Closes: #14878

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• Urgent deadline (GA date, etc.):
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SLA

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• Please give the docs team up to 1 week to review your PR unless you've added an urgent due date to it.
  Thanks in advance for your help!

PRE-MERGE CHECKLIST

Make sure you've checked the following before merging your changes:

• Checked Vercel preview for correctness, including links
• PR was reviewed and approved by any necessary SMEs (subject matter experts)
• PR was reviewed and approved by a member of the Sentry docs team

EXTRA RESOURCES

• Sentry Docs contributor guide

[vercel]

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Project	Deployment	Preview	Comments	Updated (UTC)
sentry-docs	Ready	Preview	Comment	Sep 11, 2025 10:56am

1 Skipped Deployment

Project	Deployment	Preview	Comments	Updated (UTC)
develop-docs	Ignored			Sep 11, 2025 10:56am

[codecov]

Bundle Report

Changes will increase total bundle size by 676 bytes (0.0%) ⬆️. This is within the configured threshold ✅

Detailed changes

Bundle name	Size	Change
sentry-docs-client-array-push	9.91MB	-290 bytes (-0.0%) ⬇️
sentry-docs-server-cjs	12.61MB	966 bytes (0.01%) ⬆️

Affected Assets, Files, and Routes:

view changes for bundle: sentry-docs-server-cjs

Assets Changed:

Asset Name	Size Change	Total Size	Change (%)
1729.js	-3 bytes	1.78MB	-0.0%
../instrumentation.js	-3 bytes	1.1MB	-0.0%
9523.js	-3 bytes	1.08MB	-0.0%
../app/[[...path]]/page.js.nft.json	325 bytes	805.32kB	0.04%
../app/platform-redirect/page.js.nft.json	325 bytes	805.23kB	0.04%
../app/sitemap.xml/route.js.nft.json	325 bytes	802.7kB	0.04%

view changes for bundle: sentry-docs-client-array-push

Assets Changed:

Asset Name	Size Change	Total Size	Change (%)
static/chunks/pages/_app-*.js	-3 bytes	882.71kB	-0.0%
static/chunks/8321-*.js	-3 bytes	425.87kB	-0.0%
static/media/7c239973d8aef789-*.woff2 (New)	32.56kB	32.56kB	100.0% 🚀
static/media/32c80fb7588b7a2e-*.woff2 (New)	32.48kB	32.48kB	100.0% 🚀
static/media/a5d9f2ead0568494-*.woff2 (New)	21.08kB	21.08kB	100.0% 🚀
static/media/5b25d60b4670300e-*.woff2 (New)	19.29kB	19.29kB	100.0% 🚀
static/media/fc5b975a09123a00-*.woff2 (New)	9.75kB	9.75kB	100.0% 🚀
static/media/99e31c27a1524300-*.woff2 (New)	9.35kB	9.35kB	100.0% 🚀
server/middleware-*.js	5.55kB	6.55kB	555.3% ⚠️
server/middleware-*.js	-5.55kB	1.0kB	-84.74%
static/XRenNOYrDcG8697sa8ZuH/_buildManifest.js (New)	684 bytes	684 bytes	100.0% 🚀
static/XRenNOYrDcG8697sa8ZuH/_ssgManifest.js (New)	77 bytes	77 bytes	100.0% 🚀
static/media/4fca85807f6c09f6-*.woff2 (Deleted)	-32.6kB	0 bytes	-100.0% 🗑️
static/media/d695df15e3ff125c-*.woff2 (Deleted)	-32.58kB	0 bytes	-100.0% 🗑️
static/media/acdf4f392b58827a-*.woff2 (Deleted)	-21.13kB	0 bytes	-100.0% 🗑️
static/media/501d9eeee6e2b0cc-*.woff2 (Deleted)	-19.41kB	0 bytes	-100.0% 🗑️
static/media/a72efd2c2476ebb2-*.woff2 (Deleted)	-9.7kB	0 bytes	-100.0% 🗑️
static/media/9d7436bc73437f75-*.woff2 (Deleted)	-9.36kB	0 bytes	-100.0% 🗑️
static/CYdCUq0dymluQ299YpJQ1/_buildManifest.js (Deleted)	-684 bytes	0 bytes	-100.0% 🗑️
static/CYdCUq0dymluQ299YpJQ1/_ssgManifest.js (Deleted)	-77 bytes	0 bytes	-100.0% 🗑️