Add CUB package builder and include in all Red Bear OS configs

CUB (Red Bear OS Package Builder) is a Rust CLI tool that combines package management and building:
- RBPKGBUILD parser (TOML format) with full spec support
- Cookbook adapter converting RBPKGBUILD to recipe.toml
- PKGBUILD (Arch AUR) to RBPKGBUILD conversion with Linuxism detection
- Dependency mapping (Arch to Redox names)
- pkgar package creation integration
- Build environment setup with Cookbook env vars
- CLI with pacman-style shortcuts: -S, -Ss, -B, -G, -Pi, -Sua, -Sc, --import-aur

28 cub-lib tests passing. cub-cli compiles with local pkgutils.
Added cub = {} to redbear-desktop, redbear-full, redbear-minimal configs.
Created recipe symlink and updated integrate-redbear.sh.

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

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

local/recipes/system/cub/source/cub-lib/Cargo.toml

@@ -0,0 +1,33 @@
+[package]
+name = "cub-lib"
+description = "Red Bear OS Package Builder Library"
+
+version.workspace = true
+edition.workspace = true
+license.workspace = true
+
+[lib]
+name = "cub"
+doctest = false
+
+[dependencies]
+serde = { workspace = true }
+serde_derive = { workspace = true }
+toml = { workspace = true }
+thiserror = { workspace = true }
+hex = "0.4"
+blake3 = "1"
+walkdir = "2"
+tempfile = "3"
+
+# pkgar integration for package creation
+pkgar = { version = "0.2.2", optional = true }
+pkgar-core = { version = "0.2.2", optional = true }
+pkgar-keys = { version = "0.2.2", optional = true }
+
+# HTTP for source fetching
+reqwest = { version = "0.12", default-features = false, features = ["blocking", "rustls-tls"], optional = true }
+
+[features]
+default = ["full"]
+full = ["pkgar", "pkgar-core", "pkgar-keys", "reqwest"]