fix: reset terminal prompt on session changes

[kbuffardi]

Summary

Implements the terminal-session reset behavior requested in #72.

• Adds a reset API that clears terminal output, input/history state, and workspace prompt context.
• Ensures new workspace sessions render at most one prompt, and no prompt appears before compiler readiness.
• Routes workspace transitions through the reset path without changing user-initiated clear behavior.
• Adds end-to-end coverage for clean reset and pre-readiness behavior.

Verification

• npm run lint
• npm run test:e2e (177 passing)
• npm run build

Build retains the repository’s existing webpack bundle-size warnings.

Closes #72