test(e2e): Migrate test app nextjs-turbo into nextjs-15

[chargome]

• Migrates pages router and route handler tests from nextjs-turbo to nextjs-15
• Removes the redundant nextjs-turbo test app
• All tests are now covered in nextjs-15 with turbopack variant

[github-actions]

Codecov Results 📊

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Generated by Codecov Action

[github-actions]

Codecov Results 📊

✅ 25 passed | ⏭️ 5 skipped | Total: 30 | Pass Rate: 83.33% | Execution Time: 24.05s

All tests are passing successfully.

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Generated by Codecov Action

[github-actions]

node-overhead report 🧳

Note: This is a synthetic benchmark with a minimal express app and does not necessarily reflect the real-world performance impact in an application.

Scenario	Requests/s	% of Baseline	Prev. Requests/s	Change %
GET Baseline	9,197	-	9,138	+1%
GET With Sentry	1,654	18%	1,775	-7%
GET With Sentry (error only)	5,987	65%	6,108	-2%
POST Baseline	1,135	-	1,196	-5%
POST With Sentry	550	48%	605	-9%
POST With Sentry (error only)	1,000	88%	1,054	-5%
MYSQL Baseline	3,326	-	3,343	-1%
MYSQL With Sentry	403	12%	512	-21%
MYSQL With Sentry (error only)	2,679	81%	2,707	-1%

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