Consolidate IR/index storage to a single project .codc with root HOOK.toml

[Copilot]

The storage model is now project-scoped instead of root-unit scoped: one .codc per project, no s_idx, and one shared index entry. The index is now stored as HOOK.toml at the container root (not under idx/).

• Container topology

  • Switched .codc selection from per-root-unit files to a single project container:
    • src/bin/project.codc
  • Artifact entries remain unit-qualified inside the container:
    • <unit>/<Class>.codb

• Index topology

  • Removed root-unit index partitioning and standalone s_idx fallback path.
  • Standardized on one shared in-container index entry:
    • HOOK.toml at .codc root

• Read/write path updates

  • IRManager now resolves index entry name directly to HOOK.toml (no idx/ prefix).
  • Index load/save flow now targets the single shared container index document.
  • Updated related comments/log text to reflect project-scoped container/index behavior.

src/bin/project.codc
  ├─ HOOK.toml
  ├─ math/Vector.codb
  └─ app/Main.codb