feat(pi-kit): lane transcript capture and full-screen lanes TUI

[ElbertePlinio]

What

Rescues and lands the transcript/TUI work-in-progress, rebased onto async lanes (#45).

• Raw per-lane JSONL transcripts under raw/<run>/<lane>.jsonl (LaneRunner tap)
• LaneTranscript reducer: thinking/text/tool entries for live tailing and archived replay
• Full-screen /lanes tui browser (run rail + per-lane transcript view)
• Logical line-count fix for compact read/write tool rows
• journal-core: rawRunDir, listRuns

Review fixes (second commit)

• P1: transcript polling sliced a UTF-16 string by a byte offset — silently dropped events after any non-ASCII char; now reads bytes at offset, clamps to the last complete newline, decodes after slicing
• P2: half-flushed trailing lines were consumed and lost; the newline clamp holds them for the next poll
• P3: raw.end() ran before the child's final stdout flush, truncating abandoned/failed lane transcripts; moved into the child close handler

Validation

• tsc clean, 81/81 vitest (79 + 2 new: multibyte tailing across polls, partial-line holding — both through real files and the real journal path)
• Fix-verification review: clean