feat(browser): Migrate browser profiling thread data to span attributes

[chargome]

Migrate thread.id/thread.name assignment from processEvent hook to span.setAttribute() at span start, covering legacy, trace, and manual profiling modes.

closes#20379

[github-actions]

size-limit report 📦

Path	Size	% Change	Change
@sentry/browser	26.84 kB	-	-
@sentry/browser - with treeshaking flags	25.28 kB	-	-
@sentry/browser (incl. Tracing)	44.73 kB	-	-
@sentry/browser (incl. Tracing + Span Streaming)	46.73 kB	-	-
@sentry/browser (incl. Tracing, Profiling)	49.73 kB	-0.05%	-20 B 🔽
@sentry/browser (incl. Tracing, Replay)	84.38 kB	-	-
@sentry/browser (incl. Tracing, Replay) - with treeshaking flags	73.81 kB	-	-
@sentry/browser (incl. Tracing, Replay with Canvas)	89.08 kB	-	-
@sentry/browser (incl. Tracing, Replay, Feedback)	101.71 kB	-	-
@sentry/browser (incl. Feedback)	44.03 kB	-	-
@sentry/browser (incl. sendFeedback)	31.66 kB	-	-
@sentry/browser (incl. FeedbackAsync)	36.77 kB	-	-
@sentry/browser (incl. Metrics)	27.93 kB	-	-
@sentry/browser (incl. Logs)	28.08 kB	-	-
@sentry/browser (incl. Metrics & Logs)	28.75 kB	-	-
@sentry/react	28.59 kB	-	-
@sentry/react (incl. Tracing)	47.01 kB	-	-
@sentry/vue	31.75 kB	-	-
@sentry/vue (incl. Tracing)	46.59 kB	-	-
@sentry/svelte	26.86 kB	-	-
CDN Bundle	29.24 kB	-	-
CDN Bundle (incl. Tracing)	47.16 kB	-	-
CDN Bundle (incl. Logs, Metrics)	30.61 kB	-	-
CDN Bundle (incl. Tracing, Logs, Metrics)	48.28 kB	-	-
CDN Bundle (incl. Replay, Logs, Metrics)	69.94 kB	-	-
CDN Bundle (incl. Tracing, Replay)	84.55 kB	-	-
CDN Bundle (incl. Tracing, Replay, Logs, Metrics)	85.62 kB	-	-
CDN Bundle (incl. Tracing, Replay, Feedback)	90.36 kB	-	-
CDN Bundle (incl. Tracing, Replay, Feedback, Logs, Metrics)	91.46 kB	-	-
CDN Bundle - uncompressed	85.99 kB	-	-
CDN Bundle (incl. Tracing) - uncompressed	141.47 kB	-	-
CDN Bundle (incl. Logs, Metrics) - uncompressed	90.18 kB	-	-
CDN Bundle (incl. Tracing, Logs, Metrics) - uncompressed	144.93 kB	-	-
CDN Bundle (incl. Replay, Logs, Metrics) - uncompressed	215.01 kB	-	-
CDN Bundle (incl. Tracing, Replay) - uncompressed	260.18 kB	-	-
CDN Bundle (incl. Tracing, Replay, Logs, Metrics) - uncompressed	263.62 kB	-	-
CDN Bundle (incl. Tracing, Replay, Feedback) - uncompressed	273.87 kB	-	-
CDN Bundle (incl. Tracing, Replay, Feedback, Logs, Metrics) - uncompressed	277.31 kB	-	-
@sentry/nextjs (client)	49.52 kB	-	-
@sentry/sveltekit (client)	45.23 kB	-	-
@sentry/node-core	60.84 kB	+0.02%	+11 B 🔺
@sentry/node	165.98 kB	+0.01%	+9 B 🔺
@sentry/node - without tracing	73.96 kB	+0.01%	+5 B 🔺
@sentry/aws-serverless	108.07 kB	+0.01%	+5 B 🔺
@sentry/cloudflare (withSentry) - minified	170.66 kB	-	-
@sentry/cloudflare (withSentry)	430.47 kB	-	-

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[cursor]

Cursor Bugbot has reviewed your changes and found 2 potential issues.

^{❌ Bugbot Autofix is OFF. To automatically fix reported issues with cloud agents, enable autofix in the Cursor dashboard.}

^{Reviewed by Cursor Bugbot for commit 5b98ef3. Configure here.}