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.

src/components/textarea.lisp

@@ -237,11 +237,20 @@
             (textarea-insert-char ta ch))))))))
 
 ;;; ---------------------------------------------------------------------------
-;;; Rendering (stub — proper rendering uses theme + backend)
+;;; Rendering
 ;;; ---------------------------------------------------------------------------
 (defmethod render ((ta textarea) (backend t))
-  "Render a textarea widget. Full rendering requires *current-backend*,
-  *current-theme*, and the rendering pipeline. This is a no-op stub for
-  unit testing the widget logic."
-  (declare (ignore ta backend))
-  (values))
+  "Render textarea lines at layout position."
+  (let* ((ln (textarea-layout-node ta))
+         (x (if ln (layout-node-x ln) 0))
+         (y (if ln (layout-node-y ln) 0))
+         (w (if ln (layout-node-width ln) 80))
+         (h (if ln (layout-node-height ln) 24))
+         (lines (textarea-lines ta))
+         (max-lines (min (length lines) h)))
+    (declare (ignore w))
+    (loop for i from 0 below max-lines
+          for line in lines
+          do (draw-text backend x (+ y i)
+                        (subseq line 0 (min (length line) w))
+                        nil nil))))