docs(maestro): amend DESIGN.md for draft panes (#62)

The spawn modal is no longer one of the three surfaces: the Components
section now describes the draft pane, and the stale ≥600px
bottom-sheet→dialog breakpoint note is dropped.

DESIGN.md

@@ -79,16 +79,15 @@ no bounce. Tokens `--dur-fast`/`--dur`/`--dur-slow`.
   `connecting` state pill pulses.
 - Interaction: row hover/focus, button press (1px), input focus ring, chevron
   rotation, theme-toggle sun/moon swap.
-- Modal: bottom-sheet slide-up on mobile, scale-pop on ≥600px.
 - Every animation has a `prefers-reduced-motion: reduce` path (pulses off,
   transitions near-instant).
 
 ## Layout & structure
 
 Mobile-first, structural responsiveness (not fluid type). Single `≤520px`
-breakpoint stacks the header (full-width search, wrapped actions). `≥600px`
-switches the spawn modal from bottom-sheet to centered dialog. A faint slate grid texture sits on `--bg` as
-terminal atmosphere (very low contrast, not decoration).
+breakpoint stacks the header (full-width search, wrapped actions). A faint
+slate grid texture sits on `--bg` as terminal atmosphere (very low contrast,
+not decoration).
 
 ## Components
 
@@ -101,8 +100,10 @@ Three surfaces, all DOM built in TS, styled by class:
   no-sessions, no-search-match.
 - **Attach** — header (back, `session <id>`, live/closed/error state pill) over
   a framed dark xterm with a green cursor.
-- **Spawn modal** — bottom-sheet/dialog form; mono inputs with green focus
-  ring; grouped worktree fieldset.
+- **Draft pane** — the spawn form mounted inline in an empty split pane,
+  focusable like any session pane; mono inputs with green focus ring; grouped
+  worktree fieldset. Spawn opens one (reusing an empty focused pane, else
+  splitting), and "Spawn similar" seeds one from a session's dir + command.
 
 Interactive elements ship default / hover / focus-visible / active / disabled
 states; the accent green is used only for action, selection, focus, and live
@@ -111,5 +112,5 @@ status — never decoration.
 ## Dev review aids (DEV-only, stripped from production)
 
 `web/src/mock.ts` + query params seed a representative catalog without a running
-daemon: `?mock` (seed sessions), `?mock&spawn` (open the spawn modal),
+daemon: `?mock` (seed sessions), `?mock&spawn` (open a draft pane),
 `?theme=light|dark` (pin a theme). Guarded by `import.meta.env.DEV`.