feat(emailgen): global persona pool + Date-stamped EML mtimes

Two changes that unwind earlier MazeNET-only assumptions and fix a
realism tell:

1. Persona resolution is now per-decky-source, not topology-only.  The
   scheduler walks the union view (list_running_deckies, including
   fleet MACVLAN/IPVLAN + SWARM shards) and picks the right persona
   list for each source:
     * topology decky -> Topology.email_personas (per-topology richness
       preserved)
     * fleet / shard  -> a single host-wide pool loaded from disk
       (DECNET_EMAILGEN_PERSONAS, /etc/decnet/email_personas.json, or
       ~/.decnet/email_personas.json)
   Operators install the global pool via 'decnet emailgen
   import-personas <file>' which validates with the same Pydantic
   schema the worker uses.

2. The driver now runs 'touch -d <Date>' inside the docker exec right
   after the EML write so file mtime matches the email's RFC 2822
   Date: header.  Without this an attacker 'ls -lt'ing the spool sees
   every email clustered inside the worker's tick window — the
   cluster itself was a stylometric tell.

CLI now exposes 'decnet emailgen' as a sub-app with 'run' (default,
backwards-compatible with bare 'decnet emailgen') and 'import-personas'.
list_running_deckies carries topology_id through so consumers can resolve
the parent topology without a second round-trip.

decnet/orchestrator/drivers/email.py

@@ -239,9 +239,17 @@ class EmailDriver:
         container = _container_for(
             action.mail_decky_name, list(action.mail_decky_services),
         )
+        # Stamp the file's mtime + atime to match the EML's Date: header
+        # so an attacker `ls -lt`'ing the spool doesn't see a wall of
+        # files all created within the worker's tick window — the cluster
+        # itself is a tell.  ``touch -d`` on GNU coreutils accepts RFC
+        # 2822 dates directly via the same formatdate() string we wrote
+        # into the header, so no extra parsing on the container side.
+        eml_date_header = formatdate(ts.timestamp(), localtime=False)
         sh_cmd = (
             f"mkdir -p {shlex.quote(eml_dir)} && "
-            f"tee {shlex.quote(eml_path)} >/dev/null"
+            f"tee {shlex.quote(eml_path)} >/dev/null && "
+            f"touch -d {shlex.quote(eml_date_header)} {shlex.quote(eml_path)}"
         )
         argv = [_DOCKER, "exec", "-i", container, "sh", "-c", sh_cmd]
         rc2, _stdout2, stderr2 = await _run_capture(