main: full CLI config with network/serial/file sources and JSON project export

- --network NAME HOST PORT  (repeatable)
- --serial  NAME DEVICE BAUD  (repeatable)
- --file    PATH  (repeatable, replayed via FileBackend)
- --log-dir DIR   (frame logging, default ./log)
- --delay   SECS  (file replay inter-frame delay, default 1.0)
- --project FILE  load config from JSON project file
- --save    FILE  export current config as JSON project file

Multiple source types can be combined. Network sources share one
NetworkBackend; serial sources each get their own SerialBackend;
file sources share one FileBackend. The poll loop runs only for
network sources; file-only mode joins the reader threads; serial-only
mode blocks on signal.pause().

file_backend: rename _source_id -> source_id_from_path (public),
add join() to wait for reader threads.

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

backend/file_backend.py

@@ -0,0 +1,77 @@
+import re
+import time
+from threading import Thread
+
+from backend.a_backend import ABackend
+from msg.container import MsgContainer
+
+_FILENAME_RE = re.compile(r'\d{4}_\d{2}_\d{2}_\d{2}_\d{2}_\d{2}_(.+)\.log$')
+_CHUNK = 64
+
+
+def source_id_from_path(path: str) -> str | None:
+    m = _FILENAME_RE.search(path)
+    return m.group(1) if m else None
+
+
+class FileBackend(ABackend):
+    def __init__(self, files: list[str], delay: float = 1.0):
+        self._delay = max(0.0, min(10.0, delay))
+        self._entries = [{'path': p, 'source_id': source_id_from_path(p), 'xcvr': None, 'file': None, 'thread': None}
+                         for p in files]
+        self._running = False
+
+    @property
+    def delay(self) -> float:
+        return self._delay
+
+    @delay.setter
+    def delay(self, value: float):
+        self._delay = max(0.0, min(10.0, value))
+
+    def register_xcvr(self, xcvr):
+        for e in self._entries:
+            if e['source_id'] == xcvr.name.strip():
+                e['xcvr'] = xcvr
+                xcvr.on_register(self)
+                return
+        raise Exception(f"No log file found for source \"{xcvr.name}\"")
+
+    def connect(self):
+        for e in self._entries:
+            e['file'] = open(e['path'], 'rb')
+
+    def start(self):
+        self._running = True
+        for e in self._entries:
+            e['thread'] = Thread(target=self._run, args=(e,), daemon=True)
+            e['thread'].start()
+
+    def stop(self):
+        self._running = False
+        for e in self._entries:
+            if e['thread'] and e['thread'].is_alive():
+                e['thread'].join(timeout=self._delay + 1.0)
+
+    def join(self):
+        for e in self._entries:
+            if e['thread']:
+                e['thread'].join()
+
+    def disconnect(self):
+        for e in self._entries:
+            if e['file']:
+                e['file'].close()
+                e['file'] = None
+
+    def _run(self, entry: dict):
+        xcvr = entry['xcvr']
+        f    = entry['file']
+        while self._running:
+            data = f.read(_CHUNK)
+            if not data:
+                break
+            if xcvr:
+                xcvr.on_recv(MsgContainer(data, xcvr))
+            if self._delay > 0:
+                time.sleep(self._delay)