fix(macos): report Homebrew library mismatches at launch and add a daily canary

[mcoliver]

Summary

UTV.app loads its third-party libraries from the user's Homebrew. Homebrew upgraded OpenColorIO from 2.5 to 2.6; OCIO puts its version in every C++ symbol, so the 2026.9 release aborted in dyld before running any code: no window, no log, no dialog (#85). The same happens in reverse when a new UTV is installed over older libraries.

• Launcher check. Before the real launch, the launcher starts UTV-bin -version, which loads and binds every library in under 0.1 s. If dyld fails, it reports which library does not match and the fix (brew update && brew upgrade && brew upgrade --cask utv): a dialog with "Update with Homebrew" / "Copy Command" when started from Finder, a message on stderr from a terminal. A check that cannot run, times out, or fails for any other reason never blocks the launch. UTV_SKIP_LIBRARY_CHECK=1 skips it.
• Daily canary. homebrew-canary.yml installs the current release from the tap on a clean macOS runner with that day's Homebrew, starts UTV-bin, utvio and utvls and loads every format plugin, and opens (or comments on) an issue when that fails.
• The launcher's terminal hint gave a wrong URL for the tap; fixed.
• AGENTS.md §1.5 records that the libraries are intentionally not bundled.

Verification

• Real mismatch: today's dev build (built against OCIO 2.6) on a Mac with OCIO 2.5.2. The released launcher prints only dyld's raw abort; the new launcher prints UTV could not load opencolorio 2.5.2_1, the fix command and dyld's details, and exits 1.
• A missing library ("Library not loaded") is reported the same way.
• Matching libraries: the app starts as before.
• Not verified: the Finder dialog itself (the terminal path was run; the dialog was not opened), and the canary's issue-creation step, which is skipped on pull requests.

Refs #85

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