feat(crud): complete CRUD with DELETE endpoints

[KRISHNA-24BCS127]

Summary

Completes the CRUD matrix — the DELETE operations were missing from the API. Adds permanent account deletion and teammate entry removal, wired into the dashboard UI and documented in the README.

Changes

• DELETE /api/profile — authenticated user permanently deletes their own account and all associated sessions (MongoDB + in-memory fallback).
• DELETE /api/teammates/:id — authenticated deletion of a teammate entry (moderation/cleanup), MongoDB + in-memory fallback.
• Dashboard UI — added a red "Delete Account" button with a confirm dialog next to Logout; on success it clears the token and returns to signup.
• README — API reference table updated with both new DELETE endpoints.

Validation

• Full CRUD lifecycle smoke-tested against the running server:
  • Create: signup returns 201
  • Read: login returns token; profile + teammates list return data
  • Update: profile PUT updates bio/availability
  • Delete: teammate removed; account deleted; follow-up profile/login requests correctly return 401
• All CI syntax checks pass locally (server.js, public/*.js, scripts/*, utils/*, routes/*)
• All pages boot and return 200