feat: import an asciinema terminal recording into the interaction stream

[REPPL]

Ships intent itd-11 (a terminal recording arrives the way a voice recording already does).

• testimony import -session DIR [-cast FILE] [-offset SECONDS] reads an operator-recorded asciicast (v2 absolute times or v3 intervals, accumulated on an exact microsecond grain so both formats yield identical records), anchors it to the session t0 from the header timestamp or an explicit offset, coalesces output per displayed line, splits oversized events at rune boundaries under the JSONL budget, drops input events unconditionally and reports the count, rewrites interactions.jsonl atomically replacing only its own prior records, and archives the cast as terminal.cast.
• record, merge, report, analyze, and review are unchanged; the timeline schema learns no new source type.
• New how-to for the two-terminal session with the privacy warning; reference pages, CI smoke step, and AGENTS.md updated.
• Live-verified against a real asciinema 2.4.0 (v2) recording; the 3.x line is fixture-verified only. Coloured output renders as escape residue in the report, recorded as an open ledger issue for a follow-up.
• Spec closed and intent shipped in the same change; fidelity audit ingested into the intent's Audit Notes.

Assisted-by: Claude:claude-fable-5-1