v0.4.0: Emacs bridge — passepartout.el (TCP framed protocol)

RED: extras/passepartout.el did not exist — no Emacs integration.

GREEN: Emacs bridge verified:
- elisp compiles cleanly (byte-compile-file exit 0)
- TCP connection to daemon on port 9105 succeeds
- Framed protocol receive: 6-char hex header + payload parsed correctly
- Handshake verified: (:TYPE :EVENT :PAYLOAD (:ACTION :HANDSHAKE
  :VERSION 0.3.0 :CAPABILITIES (:AUTH :ORG-AST)))
- Framed message send works (user-input transmitted)

Usage:
  M-x passepartout            — connect, open response buffer
  M-x passepartout-send-region — send selected region as user-input
  M-x passepartout-send-buffer — send entire buffer
  M-x passepartout-disconnect  — close connection

Features:
- passepartout--filter: buffers partial TCP data, extracts complete
  framed messages (handles chunk boundaries)
- passepartout--handle-message: renders agent text as Org headlines
  with timestamps, gate-trace as property drawers
- passepartout--sentinel: handles connection loss gracefully
- passepartout-response-mode: derived from special-mode, read-only

Protocol ported from core-communication.org: 6-char hex length +
prin1'd plist. Identical to TUI and CLI — daemon treats all
clients uniformly.

.gitignore

@@ -12,3 +12,4 @@ test_input.txt
 /tmp/*.lisp
 *.fasl
 docs/#DESIGN_DECISIONS.org# docs/DESIGN_DECISIONS.org~
+extras/*.elc