fix(coding-agent): re-exported relocated catalog symbols from legacy pi-ai shim

`calculateCost`, `modelsAreEqual`, and `getBundledProviders` moved from the
`@oh-my-pi/pi-ai` barrel to `@oh-my-pi/pi-catalog/models` in the catalog
split (1b9d9d0851). The legacy-extension pi-ai root shim already bridged
`getBundledModel`/`getBundledModels` back under their old `getModel`/
`getModels` names but never re-exported the other relocated symbols, so any
legacy extension importing `calculateCost` from `@oh-my-pi/pi-ai` failed
plugin validation at install time with `Export named 'calculateCost' not
found in module '.../legacy-pi-ai-shim.ts'`.

Bridge all three symbols through the shim so pre-split legacy extensions
load again. Add regression tests that load fixtures importing
`calculateCost`, `modelsAreEqual`, and `getBundledProviders` from
`@oh-my-pi/pi-ai` and assert identity against the catalog implementations.

Fixes #4584

packages/coding-agent/src/extensibility/legacy-pi-ai-shim.ts

@@ -19,7 +19,13 @@
  * `types.ts` via the `export *` below — pi-ai still exports both as types,
  * only the runtime `Type` builder and `StringEnum()` helper were removed.
  */
-import { getBundledModel, getBundledModels } from "@oh-my-pi/pi-catalog/models";
+import {
+	calculateCost,
+	getBundledModel,
+	getBundledModels,
+	getBundledProviders,
+	modelsAreEqual,
+} from "@oh-my-pi/pi-catalog/models";
 import { type TSchema, Type } from "./typebox";
 
 export interface StringEnumOptions<T extends string> {
@@ -66,8 +72,15 @@ export function StringEnum<T extends string | number>(
 }
 
 export * from "@oh-my-pi/pi-ai";
-export { Type };
-
-/** Compatibility aliases for renamed catalog functions */
+/**
+ * Compatibility re-exports for catalog symbols that pi-ai historically exposed
+ * from its own barrel prior to the `refactor(catalog)!: split model catalog
+ * from pi-ai` change. Legacy extensions still import these from the pi-ai
+ * root, so the shim bridges them through to their new home in
+ * `@oh-my-pi/pi-catalog/models`. `getModel`/`getModels` are the historical
+ * pi-ai names for `getBundledModel`/`getBundledModels`; the remaining symbols
+ * kept their names across the move.
+ */
+export { calculateCost, getBundledProviders, modelsAreEqual, Type };
 export const getModel = getBundledModel;
 export const getModels = getBundledModels;