[JFWooten4]

Summary

Implement checklist opener-0119 (§2.4, Test double-clicking PDFs in Finder) with a focused, non-destructive macOS integration test and a separate manual Finder walkthrough.

• Build a temporary, ad-hoc signed PDF-capable macOS app from the existing native opener, substituting only its scanner process path with a harmless local receipt writer. Neither the installed opener nor user scanner settings are modified.
• Open a Unicode-and-spaces PDF with /usr/bin/open -a <temporary-app> <PDF>, which routes through macOS Launch Services and its open-documents Apple event. This tests actual native application dispatch rather than calling NSApplicationDelegate.application(_:open:) directly.
• Assert that the event reaches the scan-gate subprocess, preserves the requested file path, and leaves the registered default PDF handler unchanged. The synthetic app declares itself an alternative PDF handler and is never installed as the default.
• Document a genuinely interactive Finder double-click checklist, including scan-window display, clean/blocked/cancel behavior, duplicate suppression, verification of the user's default web browser, and restoration of PDF association if the user intentionally changed it. The automated test does not pretend to click the Finder UI or require Accessibility permission.
• Run the integration on the macOS CI job; preserve all existing scanner-safety, application-selection, and other tests. No secret-bearing files are accessed.

Dependencies and scope

The existing native opener in brave-pdf-opener.swift already handles application(_:open:), duplicate suppression, and native scan progress. The existing native test calls that delegate directly; this PR adds real Launch Services event-delivery coverage. It does not overlap parallel default-PDF-handler action and verification PRs #62, #63, or #65 and does not mutate system-wide defaults.

Validation

The commit tree differs from its parent and changes only one test script, the CI workflow, the README pointer, and the manual checklist. Require successful scanner-tests and macos-build on the final integrated head before squash-merging.

A clean local checkout was attempted, but GitHub DNS resolution is unavailable in the container. The work was therefore implemented in an isolated branch through the connected GitHub account (JFWooten4); GitHub Actions supplies macOS runtime verification.