ref(browser): Use convention constants for attribute keys (#25895)

**Why:** Use shared constants for culture, profiling thread, and
background-tab attributes so these keys come from conventions.

**How to review:** Compare each imported constant with the literal it
replaces; emitted attribute names stay unchanged.

Co-authored-by: GPT-6 <codex@openai.com>

Author: msonnb

packages/browser/src/integrations/culturecontext.ts

@@ -1,3 +1,4 @@
+import { CULTURE_CALENDAR, CULTURE_LOCALE, CULTURE_TIMEZONE } from '@sentry/conventions/attributes';
 import type { CultureContext, IntegrationFn } from '@sentry/core';
 import { defineIntegration, safeSetSpanJSONAttributes } from '@sentry/core';
 import { WINDOW } from '../helpers';
@@ -22,9 +23,9 @@ const _cultureContextIntegration = (() => {
 
       if (culture) {
         safeSetSpanJSONAttributes(span, {
-          'culture.locale': culture.locale,
-          'culture.timezone': culture.timezone,
-          'culture.calendar': culture.calendar,
+          [CULTURE_LOCALE]: culture.locale,
+          [CULTURE_TIMEZONE]: culture.timezone,
+          [CULTURE_CALENDAR]: culture.calendar,
         });
       }
     },

packages/browser/src/profiling/utils.ts

@@ -1,3 +1,4 @@
+import { THREAD_ID, THREAD_NAME } from '@sentry/conventions/attributes';
 /* eslint-disable max-lines */
 import type { Client, ContinuousThreadCpuProfile, DebugImage, ProfileChunk, Span } from '@sentry/core';
 import {
@@ -306,6 +307,6 @@ export function shouldProfileSession(options: BrowserOptions): boolean {
 }
 
 export function setThreadAttributes(span: Span): void {
-  span.setAttribute('thread.id', PROFILER_THREAD_ID_STRING);
-  span.setAttribute('thread.name', PROFILER_THREAD_NAME);
+  span.setAttribute(THREAD_ID, PROFILER_THREAD_ID_STRING);
+  span.setAttribute(THREAD_NAME, PROFILER_THREAD_NAME);
 }

packages/browser/src/tracing/backgroundtab.ts

@@ -1,7 +1,7 @@
 import { debug, getActiveSpan, getRootSpan, SPAN_STATUS_ERROR, spanToJSON } from '@sentry/core';
 import { DEBUG_BUILD } from '../debug-build';
 import { WINDOW } from '../helpers';
-import { SENTRY_OP } from '@sentry/conventions/attributes';
+import { SENTRY_OP, SENTRY_CANCELLATION_REASON } from '@sentry/conventions/attributes';
 
 /**
  * Add a listener that cancels and finishes a transaction when the global
@@ -35,7 +35,7 @@ export function registerBackgroundTabDetection(): void {
           rootSpan.setStatus({ code: SPAN_STATUS_ERROR, message: cancelledStatus });
         }
 
-        rootSpan.setAttribute('sentry.cancellation_reason', 'document.hidden');
+        rootSpan.setAttribute(SENTRY_CANCELLATION_REASON, 'document.hidden');
         rootSpan.end();
       }
     });