feat(packaging): the unsigned macOS .dmg built in CI, and the docs for steps 3 and 4 (P11a step 6, macOS half)

cargo-packager's dmg format (it makes the .app first) from
deploy/packaging/packager-macos.toml, an Info.plist merged into the
generated one, build-macos.sh in portable shell (BSD sed) and a
package-macos recipe; the release workflow gets a macos job on
macos-latest that uploads the .dmg as a run artifact and attaches it on a
tag. Unsigned and not notarized: that is step 5 (the owner's Developer ID,
Q-4). The config was parsed under cargo-packager 0.11.8's strict schema on
Linux; the build itself needs the CI run. No new dependency.
docs/packaging.md (macOS rows, finding 7 resolved, the staged update),
architecture.md and testing.md describe steps 3 and 4.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HS8WZziDnyxunC23MUxrLp

justfile

@@ -273,6 +273,11 @@ package-linux version="" formats="deb,appimage,pacman":
     cargo build --release -p ledger-cli
     deploy/packaging/build-linux.sh {{version}} {{formats}}
 
+# Build the unsigned macOS .dmg (on a Mac; CI does it on a tag or dispatch)
+package-macos version="":
+    cargo build --release -p ledger-cli
+    deploy/packaging/build-macos.sh {{version}}
+
 # A release folder on this machine signed with a throwaway key; then
 # `wanderbooks update --feed file://DIR/manifest.json --trusted-key DIR/release.pub`
 # Make a local release feed to try `wanderbooks update` against