Revert "Build post chat and attachment workflows"

This reverts commit 0b920da187.

backend/migrations/005_refresh_tokens.sql

@@ -1,11 +0,0 @@
-CREATE TABLE IF NOT EXISTS refresh_tokens (
-  id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
-  user_id UUID NOT NULL REFERENCES users(id) ON DELETE CASCADE,
-  token_hash TEXT NOT NULL UNIQUE,
-  expires_at TIMESTAMPTZ NOT NULL,
-  revoked_at TIMESTAMPTZ,
-  created_at TIMESTAMPTZ NOT NULL DEFAULT now()
-);
-
-CREATE INDEX IF NOT EXISTS idx_refresh_tokens_user_id ON refresh_tokens (user_id);
-CREATE INDEX IF NOT EXISTS idx_refresh_tokens_token_hash ON refresh_tokens (token_hash);