docs: warn that COMPOSE_FILE uses ';' on Windows, ':' on Linux/macOS

Windows users following the docs hit "The system cannot find the file
specified" because COMPOSE_FILE's separator is OS-specific (':' collides
with the C: drive letter). Fix every Windows example to use ';', add an
explicit OS-separator warning in .env.example, README, DEPLOY.md and the
gpu-windows compose comment, and point users at the explicit `-f` form as
a separator-agnostic alternative.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.env.example

@@ -190,11 +190,18 @@ VOICE_SILENCE_MS=800
 JARVIS_ROLE=full
 
 # --- GPU per OS: pick the matching compose override via COMPOSE_FILE ---
-# Ubuntu (nvidia-container-toolkit / CDI):
+# IMPORTANT: the file separator is OS-specific. Linux/macOS use ":" (colon);
+# Windows uses ";" (semicolon), because ":" is taken by the drive letter (C:).
+# Using the wrong one makes Docker treat the whole string as a single missing
+# filename ("...gpu-windows.yml: The system cannot find the file specified").
+# Ubuntu / macOS (nvidia-container-toolkit / CDI):
 #   COMPOSE_FILE=docker-compose.yml:docker-compose.gpu-linux.yml
-# Windows 11 (Docker Desktop + WSL2 + NVIDIA):
-#   COMPOSE_FILE=docker-compose.yml:docker-compose.gpu-windows.yml
+# Windows 11 (Docker Desktop + WSL2 + NVIDIA) — note the ";" separator:
+#   COMPOSE_FILE=docker-compose.yml;docker-compose.gpu-windows.yml
 # Browser-only host (no GPU needed): leave COMPOSE_FILE unset (base only).
+# Default below is the Linux form; Windows users must change ":" to ";" AND
+# swap gpu-linux for gpu-windows. If unsure, comment this out and pass the
+# files explicitly: docker compose -f docker-compose.yml -f <gpu-override> ...
 COMPOSE_FILE=docker-compose.yml:docker-compose.gpu-linux.yml
 
 # --- Browser HOST (JARVIS_ROLE=browser) — e.g. this LAN machine ---