feat: add direct PTY grid with expand/select mode for text copying

Replace tmux-based grid with direct PTY rendering. Add [MAX] button
to expand a pane to fullscreen and [SEL] to enable native text
selection within the expanded pane. Esc exits select/expanded mode.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/components/direct-pane.ts

@@ -0,0 +1,74 @@
+// Lightweight terminal pane: writes raw ANSI from PTY capture directly to stdout.
+// No parsing, no FrameBuffer, no OpenTUI. Just cursor-addressed raw lines.
+
+import { onFrame, hasChanged, resetHash, type CaptureResult } from "../pty/capture"
+
+export class DirectPane {
+  screenX: number   // 1-based screen column of content area
+  screenY: number   // 1-based screen row of content area
+  width: number     // content columns
+  height: number    // content rows
+  sessionName = ""
+
+  private unsub: (() => void) | null = null
+
+  // Set by DirectGridRenderer to receive frame updates
+  onFrame: ((lines: string[], pane: DirectPane) => void) | null = null
+
+  constructor(x: number, y: number, w: number, h: number) {
+    this.screenX = x
+    this.screenY = y
+    this.width = w
+    this.height = h
+  }
+
+  attach(sessionName: string) {
+    this.detach()
+    this.sessionName = sessionName
+    resetHash(`dp_${sessionName}`)
+    this.unsub = onFrame(sessionName, (result) => {
+      if (!hasChanged(result.lines, `dp_${sessionName}`)) return
+      if (this.onFrame) this.onFrame(result.lines, this)
+    })
+  }
+
+  detach() {
+    if (this.unsub) { this.unsub(); this.unsub = null }
+    if (this.sessionName) resetHash(`dp_${this.sessionName}`)
+    this.sessionName = ""
+    this.onFrame = null
+  }
+
+  reposition(x: number, y: number, w: number, h: number) {
+    this.screenX = x
+    this.screenY = y
+    this.width = w
+    this.height = h
+  }
+
+  // Build cursor-addressed ANSI output for this pane's content.
+  // Returns a string ready for stdout.write(). No allocations beyond the string.
+  buildFrame(lines: string[]): string {
+    let out = ""
+    const x = this.screenX
+    const y = this.screenY
+    const w = this.width
+    const h = this.height
+
+    for (let row = 0; row < h; row++) {
+      // Position cursor at start of this row
+      out += `\x1b[${y + row};${x}H`
+      // Erase w characters (clears old content)
+      out += `\x1b[${w}X`
+
+      if (row < lines.length) {
+        // Write raw ANSI line from PTY (already correct width)
+        out += lines[row]
+        // Reset SGR to prevent color bleed into border
+        out += "\x1b[0m"
+      }
+    }
+
+    return out
+  }
+}