Polish chrome and rework tab-switch repaint

Module renamed github.com/harrybrwn/patterm → github.com/hjbdev/patterm
across imports.

Chrome:
- Palette redrawn with rounded box-drawing borders, accent left-bar
  for the selected item, dim hints, and a separator-aware footer.
- Tab bar grew from 1 row to 3: labels with breathing room, a dim
  argv subtitle truncated to each tab's width, and an accent thick
  underline for the focused tab with a faint divider extending across
  the rest of the host width. Layout, viewport-renderer, and screen-
  renderer tests updated for the new mainTop.
- Sidebar reuses the same palette: accent section headers, `▎`
  selection marker, `●`/`○` status glyphs, dim previews.
- Shared SGR constants moved into internal/app/style.go.

Palette input:
- Adjacent duplicate arrow events (legacy `\x1b[B` + kitty
  `\x1b[57353u` for one keypress, or two of the same form) are now
  collapsed via peekArrowEvent + chunk-level dedupe in processStdin.
- On open, push `\x1b[>0u` onto the host's kitty keyboard stack so
  palette input is in plain legacy mode regardless of what the child
  pushed (codex/ratatui pushes its own flags which had been leaking
  to the host). Popped on close.

Tab-switch repaint (repaintFocused):
- Use the emulator's SerializeVT bytes (with SGR / cursor / DECSTBM
  / tabstops) instead of plain text, fed through the per-focused
  viewport renderer so the shifter translates row positions.
- Prelude resets host SGR / DECOM / DECSTBM (pinned to viewport) /
  cursor visibility before the replay, so leftover modes from the
  previously-focused child don't distort the new snapshot.
- Re-emit the saved cursor as a child-space CUP after the
  serialized bytes so the host cursor lands at the emulator's
  actual position (overriding DECSTBM's home side-effect and the
  tabstop-setup CHA sequences) AND the renderer's vr.row/vr.col
  get re-synced via trackCSI.
- cursorShifter now carries childRows and rewrites empty
  `\x1b[r` to `\x1b[<mainTop>;<mainBottom>r` (host coords) — the
  default (1,1) shifted to (4,4) was producing a one-row scrolling
  region that scroll-exploded the replay.
- After the snapshot lands, nudge the focused child with a one-row
  PTY winsize toggle so the kernel emits SIGWINCH and ratatui-style
  TUIs throw away their diff state and emit a fresh frame.

Codex still renders incorrectly after a focus switch; see TODO.md
"Switch-back render divergence" for the deep investigation handoff.

internal/app/cursorshift.go

@@ -22,10 +22,11 @@ import (
 // CSI commands.
 type cursorShifter struct {
 	rowOffset int
+	childRows int // viewport height in child rows; used for DECSTBM resets
 
 	state     shifterState
-	buf       []byte    // bytes accumulated in current escape sequence (incl. introducer)
-	csiPrefix []byte    // private prefix bytes (?, >, =) after CSI
+	buf       []byte // bytes accumulated in current escape sequence (incl. introducer)
+	csiPrefix []byte // private prefix bytes (?, >, =) after CSI
 	pending   strings.Builder
 }
 
@@ -44,12 +45,13 @@ const (
 	stSOSPMAPCEsc
 )
 
-func newCursorShifter(rowOffset int) *cursorShifter {
-	return &cursorShifter{rowOffset: rowOffset}
+func newCursorShifter(rowOffset, childRows int) *cursorShifter {
+	return &cursorShifter{rowOffset: rowOffset, childRows: childRows}
 }
 
-func (cs *cursorShifter) SetRowOffset(off int) {
-	cs.rowOffset = off
+func (cs *cursorShifter) SetGeometry(rowOffset, childRows int) {
+	cs.rowOffset = rowOffset
+	cs.childRows = childRows
 }
 
 // Shift consumes a chunk of PTY-master bytes, applies row offsets to
@@ -209,8 +211,19 @@ func (cs *cursorShifter) emitCSI() {
 		cs.pending.WriteString(strconv.Itoa(r))
 		cs.pending.WriteByte(final)
 	case 'r':
-		// DECSTBM: top;bot. Empty resets to full region; we still
-		// shift to keep the chrome row reserved.
+		// DECSTBM: top;bot. Empty params (\x1b[r) means "reset to the
+		// full screen" from the child's point of view — for us that's
+		// the viewport, not the host's full screen. Rewriting it as
+		// (1,1)+offset would produce \x1b[4;4r, a one-row region that
+		// causes catastrophic scroll-up of the replayed snapshot.
+		if len(paramsRaw) == 0 && cs.childRows > 0 {
+			cs.pending.WriteString("\x1b[")
+			cs.pending.WriteString(strconv.Itoa(cs.rowOffset + 1))
+			cs.pending.WriteByte(';')
+			cs.pending.WriteString(strconv.Itoa(cs.rowOffset + cs.childRows))
+			cs.pending.WriteByte(final)
+			return
+		}
 		top, bot, ok := parseTwoParams(paramsRaw)
 		if !ok {
 			cs.pending.Write(cs.buf)