Local appearance and material libraries (#863)

Adds local scalar appearance and material libraries: a catalog in the io crate with safe writes, engine commands to list and apply library entries, and a library dialog in the UI, with docs.

docs/features.md

@@ -1,6 +1,6 @@
 # Features
 
-SolidCraft's commands by area, generated by `cargo xtask features` from the command registry (`solidcraft-cli commands`). **347 commands.** Planned (registered, not built yet): 6. Every command runs the same way from the toolbar, a script, `solidcraft-cli exec <id> '<json>'`, the control channel and MCP; parameters are in the [command reference](book/src/reference/commands.md) (`cargo xtask book`). Status and plans: [ROADMAP](../ROADMAP.md).
+SolidCraft's commands by area, generated by `cargo xtask features` from the command registry (`solidcraft-cli commands`). **350 commands.** Planned (registered, not built yet): 6. Every command runs the same way from the toolbar, a script, `solidcraft-cli exec <id> '<json>'`, the control channel and MCP; parameters are in the [command reference](book/src/reference/commands.md) (`cargo xtask book`). Status and plans: [ROADMAP](../ROADMAP.md).
 
 ## Sketch (99)
 
@@ -434,6 +434,14 @@ SolidCraft's commands by area, generated by `cargo xtask features` from the comm
 |---|---|---|
 | Delete Face | `face.delete` | SOLID › MODIFY |
 
+## `library.*` (3)
+
+| Command | Id | Toolbar |
+|---|---|---|
+| Inspect Local Library | `library.inspect` | – |
+| Export Design Library | `library.export` | – |
+| Apply Local Library Entry | `library.apply` | – |
+
 ## `material.*` (7)
 
 | Command | Id | Toolbar |