Clarify build targets, add GRUB live configs, clean up docs

Consolidate compile target naming (redbear-live, redbear-grub-live-full,
etc.), add config/redbear-grub-live-full.toml, make redbear-live-full-grub
a legacy alias, update build-iso.sh to support all GRUB live targets, and
sync AGENTS.md/README.md build command documentation.

config/redbear-grub-live-full.toml

@@ -0,0 +1,14 @@
+# Red Bear OS GRUB Live Full Configuration
+# Canonical GRUB-backed live ISO for the full desktop/session target.
+#
+# Build: make live CONFIG_NAME=redbear-grub-live-full
+#
+# Boot flow: UEFI → GRUB (menu) → chainload EFI/REDBEAR/redbear.efi → Redox bootloader → kernel
+# Session: graphical greeter on VT 3, text login fallback on VT 2, debug console on /scheme/debug
+#
+# The installer reads bootloader = "grub" from this config and writes:
+#   EFI/BOOT/BOOTX64.EFI     — GRUB EFI binary (primary bootloader)
+#   EFI/BOOT/grub.cfg        — GRUB menu config
+#   EFI/REDBEAR/redbear.efi  — Redox bootloader (chainload target)
+
+include = ["redbear-live.toml", "redbear-grub.toml"]

config/redbear-live-full-grub.toml

@@ -1,6 +1,7 @@
 # Red Bear OS Live Full Configuration with GRUB Boot Manager
-# Live ISO for full desktop/session target with installer-native GRUB chainload.
+# Legacy compatibility alias for the canonical GRUB full live target.
 #
-# Build: make live CONFIG_NAME=redbear-live-full-grub
+# Preferred build: make live CONFIG_NAME=redbear-grub-live-full
+# Legacy build:    make live CONFIG_NAME=redbear-live-full-grub
 
-include = ["redbear-live-full.toml", "redbear-grub.toml"]
+include = ["redbear-grub-live-full.toml"]