feat: global --dry-run and restore command (#15, #16)

[renezander030]

Closes #15. Closes #16.

#15 — global --dry-run

Every draft-mutating command now honors --dry-run. Gated at the single write choke point (saveDraft), so all ~35 write commands are covered at once: the on-disk write and the .bak snapshot are skipped, while out() stamps the JSON result with "dryRun":true so agents/scripts can distinguish a preview from a commit. translate / export --batch keep their existing dry-run behavior (they write through their own paths, not saveDraft).

$ capcut speed ./project a1b2c3 2.0 --dry-run
{"ok":true,"id":"a1b2c3...","old_speed":1,"new_speed":2,"dryRun":true}   # nothing written

#16 — restore

capcut restore <project> copies <draft>.bak back over the draft to undo the last write. Single-step (one backup generation kept); dies with a clear message when no .bak exists; honors --dry-run.

Tests & docs

• test/dry-run.test.mjs + test/restore.test.mjs — 5 tests covering: byte-identical draft after dry-run, no .bak in dry-run, real write still mutates, restore round-trip, no-.bak exits non-zero, dry-run restore is a no-op.
• Full suite 129/129 green via the pre-commit hook (build + tests).
• README (Dry-run output mode, Edit section, Troubleshooting) + CHANGELOG updated.

#17 (prune) is intentionally left for a follow-up — see its scoping comment.

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