v0.7.1

A security-hardening pass on the write-safety gate and the HTTP transport, from a full-repo
audit. Read the breaking changes first — the HTTP transport now requires a token.

Security fixes

• A dry-run can no longer permanently commit via a stacked statement. Previously,
  execute_write_query(sql="DELETE FROM t; COMMIT;", dry_run=true) sent both commands over
  the driver's simple-query protocol; the embedded COMMIT ended the dry-run's wrapping
  transaction before it could roll back, so the change was committed for real while the tool
  reported rolled_back: true — bypassing the whole mode → dry-run → yolo → user_consent
  gate. The write path now rejects multi-statement SQL before executing.

• Dry-run grants are scoped to the MCP session. A dry-run preview under one session no
  longer authorizes a commit of the identical statement from a different client. Under the
  http transport a single server process serves many clients; a grant made by one is now
  invisible to the others. stdio (one client per process) is unaffected.

• The http/SSE transport now requires authentication. It previously served every tool,
  including execute_write_query, on 127.0.0.1:8000 with no credential — any local process
  could drive writes. Every request must now carry Authorization: Bearer <token>; the token
  is minted on first start, printed to the terminal, and persisted owner-only at
  ~/.db-conn-mcp/http-token. Requests without a valid token get 401; requests whose Host
  header isn't loopback get 403 (a DNS-rebinding defense). stdio is unaffected.

Breaking / Behaviour changes

• --transport http clients must now send an auth token. After upgrading, an HTTP/SSE
  client that worked before will get 401 Unauthorized until you configure it with the
  header Authorization: Bearer <token>, where <token> is printed at server startup and
  stored at ~/.db-conn-mcp/http-token. Clients connecting from a non-loopback Host are
  refused with 403. stdio clients (the default) need no changes.

• execute_write_query now rejects SQL containing more than one statement. If you relied
  on sending several ;-separated statements in one call, split them into separate calls;
  you will otherwise get a sanitized ValueError (Multiple SQL statements are not allowed; submit a single statement.). Semicolons inside string literals, dollar-quoted bodies, and
  comments are fine — only actual statement boundaries are rejected.