Task 20 of the slice plan. Thin wrapper over the repo's intent
methods that adds two preconditions: setIntent rejects empty
trimmed text, both methods throw "note not found" when the
note id doesn't exist. Repo-level COALESCE on
intent_prompted_at preserves the first-prompt invariant
(spec §3.3); IntentService's job is just input guarding so
the IPC handler stays a one-liner.
Verification: `npx vitest run tests/unit/IntentService.test.ts`
4 passed.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
dc88da0bee