Add a `--report` flag to preview changes before writing

[idomy]

Problem

stringlift apply writes a translated copy immediately. Before trusting it on a large codebase, it helps to see what would change.

Proposal

Add a read-only --report flag that prints, per file, the strings that would be replaced and their translations — without writing anything.

Acceptance criteria

• stringlift apply <dir> --glossary map.json --report writes nothing.
• Output lists, per file, each source string -> translation.
• Strings missing from the glossary are shown as skipped.

Pointers

• src/apply.mjs already computes every replacement; report mode can reuse extract() + the glossary lookup and just print instead of writing.
• Good first issue: no changes to extraction or verification logic.