Reflect Phase B of improvise-36h: `model/`, `view/`, `workbook.rs`, and
`format.rs` now live in the `improvise-core` sub-crate under `crates/`.
- Sub-crate list expanded to describe improvise-core's scope, its
dependency on improvise-formula, and the standalone-build guarantee.
- File Inventory reorganized into a single "Core crate layers" block
covering model/view/workbook/format, with paths rooted at
`crates/improvise-core/src/`.
- Updated line/test counts to match current contents (Phase A + merge
with main brought in records mode, IndexMap-backed DataStore, etc).
No architectural change; the main crate's re-exports keep every
`crate::model`/`crate::view`/`crate::workbook`/`crate::format` path
resolving unchanged, so no "How to Find Things" table edits are needed.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>