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/input.lisp

@@ -204,10 +204,14 @@
              (make-key-event :key :escape :raw (string #\Esc)))))
       ;; CSI: ESC [ ...
       (#x5b
-       (multiple-value-bind (params final-byte) (parse-csi-params)
+       (multiple-value-bind (params final-byte raw) (parse-csi-params)
          (if (null final-byte)
              (make-key-event :key :escape :raw (string #\Esc))
-             (if (and (char= (code-char final-byte) #\M)
+             ;; SGR mouse: ESC [ < ... m/M
+             (if (and raw (plusp (length raw)) (char= (char raw 0) #\<))
+                 (or (parse-sgr-mouse raw)
+                     (make-key-event :key :unknown :raw raw))
+                 (if (and (char= (code-char final-byte) #\M)
                       (>= (length params) 3))
                  (let* ((p0 (first params)))
                    (if (zerop (logand p0 #x40))
@@ -252,7 +256,7 @@
                              ctrl  (logtest modifier 4)))
                      (make-key-event :key (or key :unknown)
                                      :ctrl ctrl :alt alt :shift shift
-                                     :raw (format nil "~C[~d~C" #\Esc param (code-char final-byte))))))))))
+                                     :raw (format nil "~C[~d~C" #\Esc param (code-char final-byte)))))))))))
       ;; ESC ESC
       (#x1b
        (make-key-event :key :escape :alt t :raw "\\e\\e"))
@@ -273,24 +277,24 @@
   (let ((b (read-raw-byte :timeout timeout)))
     (unless b
       (return-from %read-event nil))
-    (case b
-      (#x1b
+    (cond
+      ((= b #x1b)
        (%read-escape-sequence))
-      (#x09
+      ((= b #x09)
        (make-key-event :key :tab :code #x09))
-      (#x0a
+      ((= b #x0a)
        (make-key-event :key :enter :code #x0a))
-      (#x0d
+      ((= b #x0d)
        (make-key-event :key :enter :code #x0d))
-      ((#x7f #x08)
+      ((or (= b #x7f) (= b #x08))
        (make-key-event :key :backspace :code b))
       ((and (>= b #x01) (<= b #x1a))
        (let ((key (intern (string-upcase (string (code-char (+ b #x60)))) :keyword)))
          (make-key-event :key key :ctrl t :code b)))
-      (#x1c (make-key-event :key :backslash :ctrl t :code b))
-      (#x1d (make-key-event :key :rbracket :ctrl t :code b))
-      (#x1e (make-key-event :key :caret :ctrl t :code b))
-      (#x1f (make-key-event :key :underscore :ctrl t :code b))
+      ((= b #x1c) (make-key-event :key :backslash :ctrl t :code b))
+      ((= b #x1d) (make-key-event :key :rbracket :ctrl t :code b))
+      ((= b #x1e) (make-key-event :key :caret :ctrl t :code b))
+      ((= b #x1f) (make-key-event :key :underscore :ctrl t :code b))
       ((and (>= b #x20) (<= b #x7e))
        (let ((ch (code-char b)))
          (make-key-event :key (intern (string (string-upcase ch)) :keyword)