Add Red Bear OS build integration script and makefile

integrate-redbear.sh is an idempotent overlay setup script: creates symlinks for custom recipes, patches, and configs; stages branding assets and firmware into local recipe sources; writes a tag file for the build system. mk/redbear.mk wires it as a make target with Podman support.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

mk/redbear.mk

@@ -0,0 +1,16 @@
+# Red Bear OS integration — runs before repo cook and disk image creation
+# Ensures all custom recipe symlinks, patches, assets, and firmware are staged.
+
+REDBEAR_TAG=$(BUILD)/redbear.tag
+
+$(REDBEAR_TAG): FORCE
+ifeq ($(PODMAN_BUILD),1)
+	$(PODMAN_RUN) make $@
+else
+	bash -c 'export REDBEAR_TAG="$$1"; exec bash local/scripts/integrate-redbear.sh' _ '$(REDBEAR_TAG)'
+endif
+
+redbear: $(REDBEAR_TAG)
+
+redbear_clean:
+	rm -f "$(REDBEAR_TAG)"