Critical fixes: case→cond in %read-event, theme resolution, SGR mouse, scrollbox/text-input/textarea render stubs, test runner exit code, ASDF rename

CRITICAL: case b → cond in %read-event (input.lisp:280)
  case with (and ...) predicate clauses treats keys as eql-compared
  atoms — all range clauses were dead code.  Every Ctrl+letter and
  printable ASCII fell through to :unknown.  text-input/textarea
  widgets were non-functional with real terminal input.  No test
  coverage of %read-event masked this.

HIGH: Theme resolution wired (backend/modern.lisp, theme.lisp)
  sgr-fg/sgr-bg now fall back to *theme-colors* hash for semantic
  keywords (:accent, :text-muted, :background-element).  *theme-colors*
  exported from cl-tty.backend.  load-preset populates it from preset
  hex values.  Previously all themed render output was invisible.

HIGH: SGR mouse parser wired (input.lisp:210-215)
  parse-sgr-mouse was defined but never called.  Now %read-escape-sequence
  detects ESC[< prefix and routes to parse-sgr-mouse.  Mouse drags,
  releases, and scroll events now parse correctly.

MEDIUM: Rendering stubs replaced
  - scrollbox: delegates to (render child backend) with position
    offset via unwind-protect (was debug string 'child at ~D')
  - text-input: draws value/placeholder at layout position
  - textarea: draws visible lines at layout position

MEDIUM: hit-test uses component-layout-node (mouse.lisp:18-31)
  Was checking nonexistent x/y/width/height slots.  Now reads
  layout-node-x/y/w/h via component-layout-node generic.

MEDIUM: test runner exit code (run-all-tests.lisp, cl-tty.asd)
  run-all-tests.lisp exits 1 if any suite fails.
  asdf:test-system exits 1 on failure.
  Renamed :cl-tty-tests to :cl-tty/test (ASDF convention).

MEDIUM: draw-border respects x/y on simple-backend (simple.lisp:42-53)
  Was writing to cursor position only.  Now uses newlines+spaces
  to reach specified coordinates (no escape sequences needed).

LOW: TabBar truncation off-by-one fixed (tabbar.lisp:47)
  >= changed to > to avoid cutting tabs 2 chars early.

LOW: Scrollbar coordinates absolute (scrollbox.lisp:61-73)
  Scrollbar drawn at viewport-relative (0,0).  Now adds layout
  node x/y offset for correct terminal positioning.

LOW: backend-write calls finish-output (modern.lisp:169)

LOW: load-preset no longer flips theme-mode (theme.lisp:43-45)
  Mode toggle caused load-preset to load wrong variant on
  second call.

All backported to org source files (org/text-input.org,
org/scrollbox-tabbar.org) so tangling produces matching .lisp.

392 tests pass, exit code 0.

backend/modern.lisp

@@ -28,9 +28,16 @@
   '((:black . 0) (:red . 1) (:green . 2) (:yellow . 3)
     (:blue . 4) (:magenta . 5) (:cyan . 6) (:white . 7)))
 
+(defvar *theme-colors* (make-hash-table :test 'eq)
+  "Hash table mapping theme keywords to hex color strings.
+Populated by the theme system's load-preset.  Checked by sgr-fg/sgr-bg
+as a fallback when a keyword is not in *named-colors*.")
+
 (defun sgr-fg (color)
   "Return SGR foreground escape for COLOR.
-  Color can be a hex string, a keyword name, or nil."
+  Color can be a hex string, a keyword name, or nil.
+  Keywords first try *named-colors*, then fall back to *theme-colors*
+  which resolves theme semantic roles to hex strings."
   (if (null color) ""
       (cond ((and (stringp color) (char= (char color 0) #\#))
              (multiple-value-bind (r g b) (hex-to-rgb color)
@@ -39,11 +46,17 @@
              (let ((index (cdr (assoc color *named-colors*))))
                (if index
                    (format nil "~C[~dm" #\Esc (+ 30 index))
-                   "")))
+                   ;; Fall back to theme-colors hash
+                   (let ((hex (gethash color *theme-colors*)))
+                     (if hex
+                         (multiple-value-bind (r g b) (hex-to-rgb hex)
+                           (format nil "~C[38;2;~d;~d;~dm" #\Esc r g b))
+                         "")))))
             (t ""))))
 
 (defun sgr-bg (color)
-  "Return SGR background escape for COLOR."
+  "Return SGR background escape for COLOR.
+  Keywords first try *named-colors*, then fall back to *theme-colors*."
   (if (null color) ""
       (cond ((and (stringp color) (char= (char color 0) #\#))
              (multiple-value-bind (r g b) (hex-to-rgb color)
@@ -52,7 +65,12 @@
              (let ((index (cdr (assoc color *named-colors*))))
                (if index
                    (format nil "~C[~dm" #\Esc (+ 40 index))
-                   "")))
+                   ;; Fall back to theme-colors hash
+                   (let ((hex (gethash color *theme-colors*)))
+                     (if hex
+                         (multiple-value-bind (r g b) (hex-to-rgb hex)
+                           (format nil "~C[48;2;~d;~d;~dm" #\Esc r g b))
+                         "")))))
             (t ""))))
 
 (defparameter *sgr-attr-codes*
@@ -149,6 +167,7 @@
 (defmethod backend-write ((b modern-backend) string)
   (let ((stream (backend-output-stream b)))
     (write-string string stream)
+    (finish-output stream)
     (length string)))
 
 (defmethod capable-p ((b modern-backend) feature)