Remove all references to chatHistory, add a prompt property instead

[cmenon12]

Description

This removes the unused and inefficient chatHistory property from prototypes in the database, and adds a prompt string property. This will contain the text prompt used, or undefined if the JSON was updated directly.

The assistant message and timestamp in the chat history are already stored elsewhere for each prototype, and prototypes are already linked through the previousId.

This is not a breaking change but work should be done later to migrate existing prototypes, see #85.

Related issues: closes #73

Checklist before marking as ready for review

Before marking as ready for review, please check that you have:

• Added appropriate and passing tests for the changes I made.
• Not broken any existing functionality or tests.
• Not introduced any new linting or formatting errors.
• Only added new dependencies that are necessary, do not introduce security vulnerabilities, and with tilde (~) version ranges.
• Checked and resolved UI accessibility issues using Axe devtools. Unresolved issues are described above.
• Updated the documentation if necessary.

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Screenshots (if appropriate)

[Copilot]

Pull request overview

This PR successfully removes the unused chatHistory property from the prototype schema and replaces it with a simpler prompt property. The change streamlines the data model by eliminating redundant storage of information that was already captured elsewhere (assistant message and timestamp are stored in the prototype's json.explanation and timestamp fields, and prototypes are linked via previousId).

Key Changes

• Removed IChatMessage interface, chatMessageSchema, and chatHistory property from the prototype schema
• Added a new optional prompt string property to store the text prompt used for each prototype version
• Simplified prototype creation and update logic by removing chatHistory management code
• Updated tests to reflect the new data structure

Reviewed changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated 2 comments.

File	Description
src/types/schemas/prototype-schema.ts	Removed IChatMessage interface and chatHistory schema definition; added prompt as optional string property to IPrototypeData interface and schema
src/routes/prototype-routes.ts	Removed chatHistory array building logic from handleUpdatePrototype and handleCreatePrototype; added prompt property with conditional logic (set to user prompt for text input, undefined for JSON input); changed prompt to const in handleCreatePrototype
src/routes/__test__/prototype-routes.test.ts	Removed chatHistory expectations from main test case; deleted two chatHistory-specific test cases; added prompt field to test expectations
jest/mockTestData.ts	Removed chatHistory array from prototypeData1; added prompt field with sample value

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