Fix local debug builds without signing certificate

[BradGroux]

First of all, thank you for releasing this!

Summary

This updates the local debug build path so make build works on contributor machines that do not have the maintainer's Apple development team or signing certificate installed.

Root cause

The Xcode project has automatic signing configured with the maintainer's development team. That is appropriate for signed app distribution, but it makes the documented contributor command fail on a fresh checkout with:

No signing certificate "Mac Development" found

Changes

• Add debug-only Makefile signing overrides for make build and make dev.
• Default local debug builds to CODE_SIGNING_ALLOWED=NO.
• Keep the existing release, DMG, notarization, and publish targets unchanged.
• Document the unsigned debug default and the optional signed debug override in CONTRIBUTING.md.

Contributors who need a signed debug build can still run:

make build DEBUG_CODE_SIGNING_ALLOWED=YES DEBUG_DEVELOPMENT_TEAM=YOURTEAMID

Validation

• make build
• make -n release

Closes #11.

[Copilot]

Pull request overview

This PR updates the local (Debug) build workflow to avoid requiring an Apple Development signing certificate or the maintainer’s development team, so contributor builds succeed on fresh checkouts.

Changes:

• Add Debug-only xcodebuild overrides to disable code signing by default (CODE_SIGNING_ALLOWED=NO).
• Allow opting into signed Debug builds via DEBUG_CODE_SIGNING_ALLOWED=YES and DEBUG_DEVELOPMENT_TEAM=....
• Document the new default and override flags in contributor docs.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
Makefile	Adds Debug signing override variables and applies them to the build target so make build works without local signing setup.
CONTRIBUTING.md	Documents that Debug builds are unsigned by default and shows how to enable signed Debug builds with Make variables.

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