feat: warn about non-import references to moved files

The import graph only rewrites import/export-from/require. Files are
also named from markdown links, package.json fields, jest.mock strings
and tsconfig file lists, and a move that dangles those must not pass
silently. mv now scans text formats plus source strings for the moved
paths, module names and old specifier forms (word-boundary matched,
lockfiles/hidden dirs skipped) and reports each occurrence once per
line on stderr and as non_import_refs[] in --json (dry-run included).
References are never edited; exit codes are unchanged.

Also moves normalize_scope into Index (its only consumer) and the
Change/ChangedFile JSON structs into output where they are built, to
stay inside the 250-line-per-file budget.

tests/typescript/refs/.notes/refs.md

@@ -0,0 +1 @@
+stale ref: ./lib/sum

tests/typescript/refs/README.md

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+Use [sum](./lib/sum.ts) via `lib/sum`.
+See also lib/summary for text.
+Layout note: lib/ holds helpers.

tests/typescript/refs/__tests__/sum.test.ts

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+jest.mock('../lib/sum');

tests/typescript/refs/app.ts

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+import { sum } from './lib/sum';
+export const x = sum(1, 2);

tests/typescript/refs/lib/sum.ts

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+export const sum = (a: number, b: number): number => a + b;

tests/typescript/refs/lib/summary.ts

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+export const summary = 'text';

tests/typescript/refs/package-lock.json

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+{ "packages": { "x": "./lib/sum" } }

tests/typescript/refs/package.json

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+{ "name": "refs-fixture", "main": "./lib/sum.ts" }