Keep Pi integration compatible with Kimetsu v2.7

[RodCor]

What changed

• updates the canonical bundled Pi extension to Pi's current typed API
• uses SessionManager for stable Pi session ids and persisted transcript paths
• feeds Pi transcripts into Kimetsu v2.7 stop/session-end hooks
• corrects the generated Pi skill to use kimetsu brain memory add
• adds installer regressions for current session identity, transcript forwarding, and the v2.7 command surface

Why

The published Pi package vendors this asset byte-for-byte. Keeping the canonical installer copy synchronized prevents direct kimetsu plugin install pi users from retaining the old process-wide fallback session id or empty lifecycle payloads. The generated skill also referenced a command removed from the current CLI.

Impact

Direct Pi installations get the same v2.7-compatible behavior as kimetsu-pi 0.1.3: proactive retrieval, isolated Pi sessions, and transcript-backed episode/distiller hooks.

Validation

• cargo fmt --all -- --check
• cargo test -p kimetsu-chat --features pi (134 passed)
• canonical extension SHA-256 matches the kimetsu-pi package copy
• real Pi 0.84.2 + Kimetsu 2.7.0 context and transcript lifecycle smoke tests passed in the package repository