v0.0.2: modern backend — raw escape sequences

Implements the modern-backend with truecolor SGR, Unicode box-drawing
(rounded/double/single), DECICM synchronized updates, OSC 8 hyperlinks,
cursor style control, and hex color parsing.

RED: 32 checks, 5 fail (class forward-ref + test bug)
GREEN: 32/32 checks passing (100%)

- backend/modern.lisp — escape generators + modern-backend class
- backend/modern-tests.lisp — 16 test cases, 32 assertions
- backend/package.lisp — updated exports
- org/modern-backend.org — literate source

backend/package.lisp

@@ -18,5 +18,12 @@
    ;; Queries
    #:capable-p
    ;; Constructors
-   #:make-simple-backend))
+   #:make-simple-backend
+   ;; Modern backend
+   #:modern-backend #:make-modern-backend
+   ;; Internal (for testing)
+   #:sgr-fg #:sgr-bg #:sgr-attr
+   #:cursor-move-escape #:cursor-style-escape
+   #:decicm-begin #:decicm-end #:osc8-link
+   #:hex-to-rgb #:border-char))
 (in-package :cl-tui.backend)