feat: verify acceptance criteria and document sync config

Add a scan->notify->web end-to-end smoke test against a seeded :memory: DB,
fix .gitignore so the cmd/naviwatcher source dir is not excluded by the
root binary rule, and document the new sync.interval field in config.yaml.example.

docs/plans/2026-07-19-notifier-webui-sync.md

@@ -132,10 +132,10 @@ name collisions.)
 - [x] run tests - must pass before task 9
 
 ### Task 9: Verify acceptance criteria
-- [ ] run full suite `go test ./...` — all pass
-- [ ] run `go vet ./...` and `go build -o naviwatcher` — clean
-- [ ] verify scan→notify→web data flow with a seeded `:memory:`/file DB smoke check
-- [ ] verify config.yaml.example documents new `sync_interval` field
+- [x] run full suite `go test ./...` — all pass
+- [x] run `go vet ./...` and `go build -o naviwatcher` — clean
+- [x] verify scan→notify→web data flow with a seeded `:memory:`/file DB smoke check
+- [x] verify config.yaml.example documents new `sync_interval` field
 
 ### Task 10: Update documentation
 - [ ] add a short "How it works now" note to README/CLAUDE.md if present