refactor: restructure project into muxplex/ subdir with brand integration

- Move coordinator/, frontend/, Caddyfile, pyproject.toml, requirements.txt,
  docs/ into muxplex/ subdir in prep for packaging/sharing
- Add brand assets to frontend/: favicon.ico, pwa-192/512.png,
  apple-touch-icon.png, wordmark-on-dark.svg
- Update app: title → muxplex, header → wordmark SVG, brand color tokens
  in style.css, manifest.json updated with muxplex name and brand icons
- Add design system: assets/branding/tokens.css (101 CSS custom properties),
  tokens.json (127 tokens), DESIGN-SYSTEM.md (856-line spec)
- Add assets/branding/: SVG sources, rendered PNGs (icons, favicons, PWA, OG)
- Add scripts/render-brand-assets.py for reproducible PNG generation
- Add muxplex/README.md

coordinator/ttyd.py

@@ -0,0 +1,156 @@
+"""
+ttyd process lifecycle management for the tmux-web coordinator.
+
+Constants:
+    TTYD_PID_DIR  — directory for the PID file (default: ~/.local/share/tmux-web/)
+    TTYD_PID_PATH — full path to the PID file (TTYD_PID_DIR / 'ttyd.pid')
+    TTYD_PORT     — port ttyd listens on (7682)
+
+Module state:
+    _active_process — the currently running ttyd subprocess (or None)
+
+Public API:
+    spawn_ttyd(session_name)  — spawn ttyd attached to a tmux session, write PID file
+    kill_ttyd()               — kill the running ttyd process, clean up PID file
+    kill_orphan_ttyd()        — kill any orphaned ttyd from a previous coordinator run
+"""
+
+import asyncio
+import os
+import signal
+import time
+from pathlib import Path
+
+# ---------------------------------------------------------------------------
+# Paths and constants
+# ---------------------------------------------------------------------------
+
+_default_ttyd_pid_dir = Path.home() / ".local" / "share" / "tmux-web"
+TTYD_PID_DIR: Path = Path(os.environ.get("TMUX_WEB_STATE_DIR", _default_ttyd_pid_dir))
+TTYD_PID_PATH: Path = TTYD_PID_DIR / "ttyd.pid"
+
+TTYD_PORT: int = 7682
+
+# ---------------------------------------------------------------------------
+# Module state
+# ---------------------------------------------------------------------------
+
+_active_process: asyncio.subprocess.Process | None = None
+
+# ---------------------------------------------------------------------------
+# Public API
+# ---------------------------------------------------------------------------
+
+
+async def kill_ttyd() -> bool:
+    """Kill the running ttyd process and clean up the PID file.
+
+    Reads the PID from TTYD_PID_PATH.  If no PID file exists, returns False.
+    If the file content is not a valid integer, removes the file and returns False.
+
+    Checks whether the process is alive via ``os.kill(pid, 0)``.  If the
+    process is already gone (ProcessLookupError), cleans up and returns True.
+    Otherwise sends SIGTERM and polls every 0.1 s for up to 2 s waiting for
+    the process to exit.  The PID file and ``_active_process`` are cleared in
+    all cases before returning.
+
+    Uses ``asyncio.sleep`` for polling to avoid blocking the event loop.
+
+    Returns:
+        True  — process was killed or was already dead.
+        False — no PID file found, or PID file contained invalid content.
+    """
+    global _active_process
+
+    if not TTYD_PID_PATH.exists():
+        return False
+
+    try:
+        pid = int(TTYD_PID_PATH.read_text().strip())
+    except ValueError:
+        TTYD_PID_PATH.unlink(missing_ok=True)
+        return False
+
+    # Check whether the process is still alive.
+    try:
+        os.kill(pid, 0)
+    except ProcessLookupError:
+        # Already dead — clean up and report success.
+        TTYD_PID_PATH.unlink(missing_ok=True)
+        _active_process = None
+        return True
+
+    # Process is alive — ask it to terminate.
+    os.kill(pid, signal.SIGTERM)
+
+    # Poll up to 2 s for the process to exit, yielding to the event loop each iteration.
+    deadline = time.time() + 2.0
+    while time.time() < deadline:
+        try:
+            os.kill(pid, 0)
+        except (ProcessLookupError, PermissionError):
+            break
+        await asyncio.sleep(0.1)
+
+    # Always clean up regardless of whether the process exited in time.
+    TTYD_PID_PATH.unlink(missing_ok=True)
+    _active_process = None
+    return True
+
+
+async def kill_orphan_ttyd() -> bool:
+    """Kill any orphaned ttyd process left over from a previous coordinator run.
+
+    On coordinator startup, checks for a stale PID file from a previous run.
+    If found, kills the process (if still running) and removes the PID file.
+    Prevents two ttyd instances running simultaneously after a coordinator
+    restart or crash.
+
+    Delegates to kill_ttyd() for all process management and PID file cleanup.
+
+    Returns:
+        True  — an orphan was found (process was dead or alive).
+        False — no PID file found, or PID file contained invalid content.
+    """
+    return await kill_ttyd()
+
+
+async def spawn_ttyd(session_name: str) -> asyncio.subprocess.Process:
+    """Spawn a ttyd process attached to *session_name* via ``tmux attach``.
+
+    Runs::
+
+        ttyd -W -m 3 -p 7682 tmux attach -t <session_name>
+
+    stdout and stderr are discarded (DEVNULL).  The PID is written to
+    TTYD_PID_PATH.  The process handle is stored in ``_active_process``.
+
+    Args:
+        session_name: The tmux session name to attach to.
+
+    Returns:
+        The asyncio.subprocess.Process object for the spawned ttyd.
+    """
+    global _active_process
+
+    proc = await asyncio.create_subprocess_exec(
+        "ttyd",
+        "-W",
+        "-m",
+        "3",
+        "-p",
+        str(TTYD_PORT),
+        "tmux",
+        "attach",
+        "-t",
+        session_name,
+        stdout=asyncio.subprocess.DEVNULL,
+        stderr=asyncio.subprocess.DEVNULL,
+    )
+
+    # Write PID file (create parent dirs if needed)
+    TTYD_PID_DIR.mkdir(parents=True, exist_ok=True)
+    TTYD_PID_PATH.write_text(str(proc.pid))
+
+    _active_process = proc
+    return proc