Add locale parameter to blueprints endpoint

[epeicher]

Summary

• Add locale parameter to /studio-app/blueprints endpoint call to support translated blueprint descriptions
• Pass user's configured locale from the i18n store to the blueprints API query

Changes

• Modified getBlueprints query in wpcom-api to accept optional locale parameter
• Updated blueprint fetching in add-site flow to pass current user locale
• Ensures blueprint descriptions are returned in the user's configured language

Test plan

• Verify blueprints load correctly with default locale (English)
• Change language in settings and verify blueprints request includes locale parameter
• Confirm blueprint descriptions are displayed in the selected language

Related

• Task: stu-1154

🤖 Generated with Claude Code

[wpmobilebot]

📊 Performance Test Results

Comparing 8437619 vs trunk

site-editor

Metric	trunk	8437619	Diff	Change
load	7711.00 ms	4860.00 ms	-2851.00 ms	🟢 -37.0%

site-startup

Metric	trunk	8437619	Diff	Change
siteCreation	9149.00 ms	9076.00 ms	-73.00 ms	🟢 -0.8%
siteStartup	3956.00 ms	3958.00 ms	+2.00 ms	🔴 0.1%

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Results are median values from multiple test runs.

Legend: 🟢 Improvement (faster) | 🔴 Regression (slower) | ⚪ No change