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/dialog.lisp

@@ -1,17 +1,11 @@
-;;; dialog.lisp — Dialog System + Toast for cl-tty
-
 (in-package :cl-tty.dialog)
 
-;; ─── Special variables ────────────────────────────────────────────────────────
-
 (defvar *dialog-stack* nil
   "Stack of active dialogs. (list) of dialog instances.")
 
 (defvar *toasts* nil
   "List of active toast notifications.")
 
-;; ─── Dialog class ─────────────────────────────────────────────────────────────
-
 (defclass dialog ()
   ((title :initarg :title :accessor dialog-title)
    (size :initarg :size :initform :medium :accessor dialog-size)
@@ -53,8 +47,6 @@
         (funcall (dialog-on-dismiss dialog)))
       dialog)))
 
-;; ─── Dialog sub-classes ──────────────────────────────────────────────────────
-
 (defun alert-dialog (title message)
   (make-instance 'dialog
     :title title
@@ -96,8 +88,6 @@
                             (pop-dialog)
                             (when on-submit (funcall on-submit value))))))
 
-;; ─── Toast system ─────────────────────────────────────────────────────────────
-
 (defclass toast ()
   ((message :initarg :message :accessor toast-message)
    (variant :initarg :variant :initform :info :accessor toast-variant)))