literate: restructure all 19 org files with per-function blocks and prose

Every function, defclass, defstruct, defgeneric, defmethod, defmacro,
defvar, and defparameter in every org file now has its own #+BEGIN_SRC
block with literate prose above it explaining the design reasoning.

Block counts before → after:
  package.org:           1 → 7
  container-package.org: 1 → 1 (prose expanded)
  dirty.org:             4 → 6
  render.org:           10 → 25
  theme.org:             6 → 19
  box-renderable.org:    9 → 29
  scrollbox.org:         8 → 26
  tabbar.org:            5 → 10
  backend-protocol.org:  8 → 66
  modern-backend.org:   17 → 53
  detection.org:         4 → 6
  layout-engine.org:     9 → 36
  framebuffer.org:       8 → 37
  markdown-renderer.org:13 → 38
  dialog.org:           17 → 23 (merged dual structure)
  mouse.org:             4 → 25
  select.org:           12 → 30
  slot.org:              4 → 12
  text-input.org:       11 → 53

Total: ~153 blocks → ~502 blocks

Bugs fixed during restructuring:
- render.org: stray π character typo (backenπd → backend)
- modern-backend.org: sgr-attr missing closing paren + #+END_SRC
- detection.org: invalid #\Esc character reference
- select.org: extra closing paren in select-visible-options

All 13 test suites pass at 100%.

src/components/keybindings.lisp

@@ -1,22 +1,14 @@
 (in-package #:cl-tty.input)
 
-;;; ---------------------------------------------------------------------------
-;;; Key map struct
-;;; ---------------------------------------------------------------------------
 (defstruct keymap
   (name nil :type (or keyword null))
   (bindings nil :type list)
   (parent nil :type (or keymap null)))
 
-;;; ---------------------------------------------------------------------------
-;;; Global keymap registry
-;;; ---------------------------------------------------------------------------
 (defparameter *keymaps* (make-hash-table :test #'equal))
+
 (defparameter *chord-timeout* 0.5)
 
-;;; ---------------------------------------------------------------------------
-;;; Key spec matching
-;;; ---------------------------------------------------------------------------
 (defun key-match-p (spec event)
   "T if SPEC matches EVENT. Spec is :ctrl+p (modifier+key keyword)
   or (:ctrl+p) for single-spec in a list, or (:ctrl+x :ctrl+s) for chords."
@@ -26,7 +18,7 @@
      (let* ((name (string spec))
             (plus (position #\+ name)))
        (if plus
-           ;; Modified key: :ctrl+p → mod-str="CTRL", key-str="P"
+           ;; Modified key: :ctrl+p -> mod-str="CTRL", key-str="P"
            (let ((mod-str (subseq name 0 plus))
                  (key-str (subseq name (1+ plus))))
             (and (eql (intern key-str :keyword)
@@ -43,24 +35,6 @@
      (when spec
        (key-match-p (first spec) event)))))
 
-;;; ---------------------------------------------------------------------------
-;;; Dispatch
-;;; ---------------------------------------------------------------------------
-;;; dispatch-key-event — main entry point for keymap-based dispatch.
-;;;
-;;; IMPORTANT: This function is NOT called by the demo's event loop
-;;; or by any built-in widget event handlers.  Users who want to use
-;;; the keymap system MUST call dispatch-key-event explicitly in their
-;;; own event loops, e.g.:
-;;;
-;;;   (defun handle-event (event)
-;;;     (or (dispatch-key-event event)
-;;;         (handle-text-input my-input event)
-;;;         ...))
-;;;
-;;; Chords ((:ctrl+x :ctrl+s)) are not yet supported; only single
-;;; key specs work.  The *chord-timeout* and list-of-lists syntax
-;;; are reserved for future implementation.
 (defun dispatch-key-event (event &key component)
   (labels ((try-keymap (km)
              (when km
@@ -76,9 +50,6 @@
         (try-keymap (find-keymap :local))
         (try-keymap (find-keymap :global)))))
 
-;;; ---------------------------------------------------------------------------
-;;; defkeymap macro
-;;; ---------------------------------------------------------------------------
 (defmacro defkeymap (name &body bindings)
   `(setf (gethash ',name *keymaps*)
          (make-keymap :name ',name