feat: add MiMo Code platform support

[matintohidi]

Summary

• Adds MiMo Code as a supported platform for graphify
• Users can now install and use graphify with MiMo Code (graphify install --platform mimo)
  Changes
• tools/skillgen/platforms.toml — Added [platform.mimo] configuration (split bundle, agent-tool-disk dispatch, verbose extraction)
• graphify/main.py — Registered "mimo" in _PLATFORM_CONFIG with skill destination at .mimo/skills/graphify/SKILL.md, added to project install/uninstall handlers
• tools/skillgen/gen.py — Added v8 baseline reference for mimo (post-v8 platform, reuses claude's skill body)
• README.md — Added MiMo Code to the supported platforms list and install command tables
• graphify/skill-mimo.md + graphify/skills/mimo/references/ — Generated skill files via skillgen
• tools/skillgen/expected/ — Added expected snapshots for drift detection
  Install
  graphify install --platform mimo
  Test plan
• uv run pytest tests/test_install.py -q — 81 passed
• uv run pytest tests/test_skillgen.py -q — 57 passed
• Skill files generated and blessed into expected/

Closes #1495