docs(io): note improvise-io layout in repo-map

Reflect improvise-8zh: `persistence/` and `import/` now live in the
`improvise-io` sub-crate under `crates/`.

- Sub-crate list expanded to describe improvise-io's scope, its
  dependencies (improvise-core, improvise-formula), and the
  standalone-build guarantee.
- File Inventory reorganized: "Import layer" + persistence entries
  collapsed into a single "I/O crate layers" block with paths rooted at
  `crates/improvise-io/src/`.
- Updated line/test counts to current contents.
- Top-level block trimmed (persistence/format no longer live there) and
  lib.rs annotated as a re-export facade.

No consumer-facing path changes; `crate::persistence::*` and
`crate::import::*` still resolve via the main crate's re-exports.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

context/repo-map.md

@@ -6,6 +6,7 @@ Library + binary crate: `src/lib.rs` re-exports public modules (many from sub-cr
 Sub-crates live under `crates/`:
 - `crates/improvise-core/` — pure-data core: `Model`, `View`, `Workbook`, and number formatting. Depends on `improvise-formula`. Re-exported from the main crate so `crate::model`, `crate::view`, `crate::workbook`, `crate::format` still resolve everywhere. Has no awareness of UI, I/O, or commands — builds standalone via `cargo build -p improvise-core`.
 - `crates/improvise-formula/` — formula parser, AST (`Expr`, `BinOp`, `AggFunc`, `Formula`, `Filter`), `parse_formula`. Re-exported as `crate::formula` from the main crate via `pub use improvise_formula as formula;`.
+- `crates/improvise-io/` — `.improv` persistence (parse/format, save/load, CSV export) and import pipeline (CSV/JSON wizard, field analyzer). Depends on `improvise-core` and `improvise-formula`; has no UI or command code. Re-exported from the main crate so `crate::persistence` and `crate::import` still resolve everywhere. Builds standalone via `cargo build -p improvise-io`.
 
 ---
 
@@ -453,22 +454,32 @@ command/cmd/                       Cmd trait, CmdContext, CmdRegistry, 40+ comma
   12 /  0t  ui/mod.rs
 ```
 
-### Import layer
+### I/O crate layers (sub-crate `improvise-io` under `crates/`)
+All of `persistence/` and `import/` now live under `crates/improvise-io/src/`.
+Paths below are relative to that root. The main crate re-exports each
+as `crate::persistence` and `crate::import` via `src/lib.rs`, so every
+consumer path stays unchanged.
+
+#### Persistence
 ```
- 773 / 38t  import/wizard.rs       ImportPipeline + ImportWizard
+ 124 /  0t  persistence/improv.pest  PEG grammar — single source of truth for .improv format
- 292 /  9t  import/analyzer.rs     Field kind detection (Category/Measure/Time/Skip)
+2410 / 83t  persistence/mod.rs       .improv save/load (pest parser + format + gzip + legacy JSON), export_csv
- 244 /  8t  import/csv_parser.rs   CSV parsing, multi-file merge
+```
+
+#### Import
+```
+1117 / 38t  import/wizard.rs         ImportPipeline + ImportWizard
+ 292 /  9t  import/analyzer.rs       Field kind detection (Category/Measure/Time/Skip)
+ 300 /  8t  import/csv_parser.rs     CSV parsing, multi-file merge
    3 /  0t  import/mod.rs
+  16 /  0t  lib.rs                   Module decls + re-exports of improvise-core/formula modules
 ```
 
 ### Top-level
 ```
  400 /  0t  draw.rs                TUI event loop (run_tui), frame composition
  391 /  0t  main.rs                CLI entry (clap): open, import, cmd, script
-  10 /  0t  lib.rs                 Public module exports (enables examples)
+  10 /  0t  lib.rs                 Public module re-exports (routes to sub-crates)
- 228 / 29t  format.rs              Number display formatting (view-only rounding)
- 124 /  0t  persistence/improv.pest PEG grammar — single source of truth for .improv format
-2291 / 83t  persistence/mod.rs     .improv save/load (pest parser + format + gzip + legacy JSON)
 ```
 
 ### Examples