fix: standardize remaining clarify prompts

[rlippmann]

What changed

• Standardized the remaining clarify prompt_to_user strings in the directive spec for Section 9 cases 1-6 and 10.
• Aligned engine clarify outputs to those canonical strings without changing directive parsing, state transitions, or pending-clarification behavior.
• Updated exact-string tests for engine and REPL prompt rendering to match the standardized text.
• Added focused REPL assertions for missing canonical clarify pass-through cases.
• Added a new soft-regression behavioral examples test file for examples 03/04/05/06, using branch/call-level assertions rather than transcript snapshots.

Why this change was needed

• Cases 1-6 and 10 were previously implementation-defined in the spec, which left prompt text non-canonical.
• Standardizing and asserting these prompts closes contract gaps between spec, engine output, and REPL/user-facing rendering.
• The added example behavior tests provide lightweight host-pattern regression protection without duplicating the full core conformance suite.