Improve DX and test-cases on seroval mode

[atilafassina]

• Keep "js" as the default for V1
• Add warnings and JSDoc for configuration options
• Add a fixture to easily swap between modes and test them out

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Latest commit: 950405a

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commit: 950405a

[Copilot]

Pull request overview

This PR improves the developer experience for working with Seroval serialization modes in SolidStart. It maintains "js" as the default serialization mode for V1 compatibility while adding comprehensive documentation and a dedicated fixture application for testing different serialization behaviors.

Changes:

• Added JSDoc documentation for the serialization.mode configuration option with warnings about V2 default changes
• Refactored serialization mode configuration to use a single variable across all router configurations
• Created a new serialization-modes fixture app to demonstrate and test CSP compatibility with different serialization modes
• Added middleware with security headers to the tests app

Reviewed changes

Copilot reviewed 18 out of 22 changed files in this pull request and generated 9 comments.

Show a summary per file

File	Description
packages/start/config/index.js	Refactored to use a single serializationMode variable instead of repeating the default logic
packages/start/config/index.d.ts	Added comprehensive JSDoc documentation for serialization mode configuration
pnpm-workspace.yaml	Added fixture subdirectories to workspace packages
pnpm-lock.yaml	Added dependencies for new fixtures (shieldwall, date-fns, marked, unstorage, csp-header)
apps/tests/src/middleware.ts	Added security middleware using shieldwall (CSP, CSRF protection)
apps/tests/src/routes/actions/use-submission.tsx	Added test case for useSubmission hook
apps/fixtures/serialization-modes/*	Complete new fixture app demonstrating serialization mode differences and CSP interactions

Files not reviewed (1)

• pnpm-lock.yaml: Language not supported

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