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/sessions.py

@@ -0,0 +1,139 @@
+"""
+tmux session enumeration and snapshot helpers for the tmux-web coordinator.
+
+In-memory cache:
+    _session_list  — most-recently-enumerated list of session names.
+    _snapshots     — most-recently-captured pane text, keyed by session name.
+
+Public API:
+    get_session_list()                    → list[str]
+    get_snapshots()                       → dict[str, str]
+    update_session_cache(names, snapshots) → None
+    run_tmux(*args)                       → str   (raises RuntimeError on nonzero exit)
+    enumerate_sessions()                  → list[str]
+    capture_pane(name, lines)             → str
+    snapshot_all(names)                   → dict[str, str]
+"""
+
+import asyncio
+
+# ---------------------------------------------------------------------------
+# In-memory cache
+# ---------------------------------------------------------------------------
+
+_session_list: list[str] = []
+_snapshots: dict[str, str] = {}
+
+
+def get_session_list() -> list[str]:
+    """Return a copy of the cached session name list."""
+    return list(_session_list)
+
+
+def get_snapshots() -> dict[str, str]:
+    """Return a copy of the cached pane-snapshot dict."""
+    return dict(_snapshots)
+
+
+def update_session_cache(names: list[str], snapshots: dict[str, str]) -> None:
+    """Replace the in-memory caches with fresh data.
+
+    Sets _session_list to *names* and _snapshots to the provided *snapshots* dict.
+    Callers must pass the return value of snapshot_all() as *snapshots*.
+    """
+    global _session_list, _snapshots
+    _session_list = list(names)
+    _snapshots = snapshots
+
+
+# ---------------------------------------------------------------------------
+# Subprocess helpers
+# ---------------------------------------------------------------------------
+
+
+async def run_tmux(*args: str) -> str:
+    """Run `tmux <args>` in a subprocess and return stdout as a string.
+
+    Raises:
+        RuntimeError: If the process exits with a nonzero return code.
+                      The error message contains the decoded stderr output.
+    """
+    proc = await asyncio.create_subprocess_exec(
+        "tmux",
+        *args,
+        stdout=asyncio.subprocess.PIPE,
+        stderr=asyncio.subprocess.PIPE,
+    )
+    stdout_bytes, stderr_bytes = await proc.communicate()
+    if proc.returncode != 0:
+        raise RuntimeError(stderr_bytes.decode("utf-8", errors="replace"))
+    return stdout_bytes.decode("utf-8", errors="replace")
+
+
+# ---------------------------------------------------------------------------
+# Session enumeration
+# ---------------------------------------------------------------------------
+
+
+async def enumerate_sessions() -> list[str]:
+    """Return the list of currently running tmux session names.
+
+    Calls ``tmux list-sessions -F #{session_name}``, splits on newlines,
+    and strips whitespace from each entry.
+
+    Returns [] if tmux is not running (RuntimeError from run_tmux).
+    """
+    try:
+        output = await run_tmux("list-sessions", "-F", "#{session_name}")
+    except RuntimeError:
+        return []
+
+    names = [line.strip() for line in output.splitlines() if line.strip()]
+    return names
+
+
+# ---------------------------------------------------------------------------
+# Pane capture
+# ---------------------------------------------------------------------------
+
+
+async def capture_pane(session_name: str, lines: int = 30) -> str:
+    """Capture the last *lines* lines of output from *session_name*.
+
+    Returns the captured text, or '' on any error.
+    """
+    try:
+        return await run_tmux(
+            "capture-pane",
+            "-p",
+            "-t",
+            session_name,
+            "-S",
+            f"-{lines}",
+        )
+    except RuntimeError:
+        return ""
+
+
+async def snapshot_all(names: list[str]) -> dict[str, str]:
+    """Capture all sessions concurrently and return a name→text mapping.
+
+    Uses asyncio.gather with return_exceptions=True so that individual
+    failures do not abort the whole batch.  Failed sessions map to ''.
+
+    Note: this function does not mutate module state — it does not update the module cache.
+    Callers are responsible for passing the result to update_session_cache.
+    """
+    if not names:
+        return {}
+    results = await asyncio.gather(
+        *[capture_pane(name) for name in names],
+        return_exceptions=True,
+    )
+    snapshots: dict[str, str] = {}
+    for name, result in zip(names, results):
+        if isinstance(result, BaseException):
+            snapshots[name] = ""
+        else:
+            snapshots[name] = result
+    return snapshots