macOS: add a launcher shim so a cold Finder open also works (#1039)

The previous commit's Apple Event handler only ever catches an open
sent to an already-running process. A cold double-click (app not
running yet) still failed: every registration point tried inside the
real binary — before app::run(), on the Subscription's first poll,
even the literal first statement of main() — reliably caught a warm
open but never the original cold-launch event. A raw
AEInstallEventHandler in a separate, minimal, non-AppKit process (no
winit/iced, just a manual CFRunLoopRunInMode pump) still missed it
too, ruling out "the real binary's heavy dependency graph loading
before main() wins the race" as the explanation.

What does reliably catch a cold launch, verified against real
Finder-equivalent opens: a from-scratch NSApplication with its own
delegate implementing application:openURLs: — in a process where we
own setDelegate: from the start, with no contention over the single
delegate slot winit already claims. That has to be a separate process
from the real GUI binary (only one -[NSApplication run] call can own a
process), so src/bin/ocs_launcher.rs is now the .app's actual
CFBundleExecutable: a small, dependency-light binary (no iced, wgpu,
or cadkernel) whose only job is to catch the open and relay it.

Relaying by replacing this process's image (exec, same PID) or by
spawning a child and exiting turned out to both be dead ends: Launch
Services tracks "the running instance of this bundle" by the
Application Serial Number it handed out to whichever process it
actually launched — this launcher, not whatever it execs into or
spawns. Once the launcher's own ASN stopped pointing at a live,
listening process, every later open Finder tried to deliver silently
went nowhere (measured with lsappinfo against a real second "Open
With", not assumed). So the launcher now stays running for the app's
session — invisible, via NSApplicationActivationPolicyAccessory, since
it owns no window — and relays every open (cold or warm) over the same
channel a second CLI invocation already uses: io::single_instance.

That relay only worked once single_instance's rendezvous key stopped
being computed from the running executable's own path. That was fine
when one binary always did the job, but the launcher and the real
binary are different executables and independently computed different
ports, so they could never find each other. Anchor the key on the
enclosing .app bundle instead, shared by both.

packaging/build_macos_signed.sh and .github/workflows/release.yml now
build ocs_launcher and place it at Contents/MacOS/OpenCADStudio (the
CFBundleExecutable Info.plist already names), with the real GUI binary
renamed to Contents/MacOS/OpenCADStudio-App alongside it.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.github/workflows/release.yml

@@ -337,6 +337,9 @@ jobs:
         run: |
           cargo build --locked --release --target aarch64-apple-darwin
           cargo build --locked --release --target aarch64-apple-darwin -p dwg-thumbnailer
+          # The launcher shim is the .app's actual CFBundleExecutable (#1039)
+          # — see src/bin/ocs_launcher.rs for why.
+          cargo build --locked --release --target aarch64-apple-darwin --bin ocs_launcher
 
       - name: Build .icns from SVG
         run: |
@@ -395,8 +398,13 @@ jobs:
           APP=OpenCADStudio.app
           rm -rf "$APP"
           mkdir -p "$APP/Contents/MacOS" "$APP/Contents/Resources" "$APP/Contents/PlugIns"
-          cp target/aarch64-apple-darwin/release/OpenCADStudio "$APP/Contents/MacOS/OpenCADStudio"
-          chmod +x "$APP/Contents/MacOS/OpenCADStudio"
+          # The launcher is CFBundleExecutable (Finder always launches it,
+          # for both document opens and plain launches); it execs into the
+          # real GUI binary, renamed alongside it, over argv. See
+          # src/bin/ocs_launcher.rs.
+          cp target/aarch64-apple-darwin/release/ocs_launcher "$APP/Contents/MacOS/OpenCADStudio"
+          cp target/aarch64-apple-darwin/release/OpenCADStudio "$APP/Contents/MacOS/OpenCADStudio-App"
+          chmod +x "$APP/Contents/MacOS/OpenCADStudio" "$APP/Contents/MacOS/OpenCADStudio-App"
           cp AppIcon.icns "$APP/Contents/Resources/AppIcon.icns"
           cp DWG.icns DXF.icns "$APP/Contents/Resources/"
           # QuickLook thumbnail extension.