Cleanup dead code and sensitive env confusion

[anthuanvasquez]

Context

The codebase has potential dead paths and confusing env configuration values.

Problem

• Potentially unused artifacts increase maintenance cost (app/random.vue, app/composables/useGetFetch.ts, chat types duplication).
• .env.example includes NUXT_PUBLIC_CHAT_SESSION_SECRET, which suggests exposing a secret publicly.

Proposed Solution

• Confirm usage and remove/relocate dead files/types.
• Fix .env.example to avoid public secret confusion.
• Update docs to reflect the final env contract.

Acceptance Criteria

• Dead/unused artifacts removed or justified
• Public secret-like env removed/renamed
• Documentation updated accordingly

Notes

Keep this strictly as cleanup; do not mix with major refactors.