v1.1.4

A display fix plus review-round docs and tests (Gemini finding 3; external
review round 5).

• Fixed Frame.String() no longer renders a bogus " (:0)" location for
  unresolved frames (both File and Line zero — e.g. the "unknown"
  sentinel a zero-value Error resolves to). A frame with either part set
  still prints the location.
• Docs External-review (round 5) drift swept: DESIGN.md §9's RetryDelay
  spec now carries the v1.1.2 CheckValid gate (delays outside the protobuf
  Duration range are rejected, not saturated); the §6 verb table gains the
  unknown-verb fallback row; problem.Write documents that a panicking
  MarshalJSON on a public field value propagates (matching encoding/json).
• Tests Previously uncovered branches pinned: %+v on a nil *Error
  ("<nil>"), the unknown-verb %v fallback, and Wrapf's non-nil path.