docs(Mountain): Rework CHANGELOG to prose format, add v2.2 section

Restructure the Mountain CHANGELOG from itemized bullet points to narrative prose paragraphs, improving readability while preserving all historical content. Add new v2.2 section documenting bundled-electron correctness pass including: JSON-RPC -32004 for benign 404s, deferred-no-op file watching, canonical-path comparison for Volumes mounts, Identifier field on SCM provider DTO, sky:replay-events handler, 64KB terminal ring buffer, and tree:getChildren timeout reduction.

The new format emphasizes user-facing impact over file references, making it more useful for release notes and external communication.

Author: NikolaRHristov