feat(realism): synthetic_files table + planner wiring + scheduler swap

Stage 3 of the realism migration. Replaces orchestrator/scheduler.py's
hardcoded _FILE_TEMPLATES/_USERS (3 templates emitting epoch-suffixed
filenames like notes-1777315854.txt with identical bodies per
template) with a persona-driven realism engine.

New surface:

- SyntheticFile SQLModel (synthetic_files table, UNIQUE on
  decky_uuid+path) — per-(decky, path) state for the future
  edit-in-place flow. Pre-v1, no _migrate_* helper.
- BaseRepository methods: record_synthetic_file,
  update_synthetic_file, list_synthetic_files,
  pick_random_synthetic_file_for_edit (used by stage 3b).
- realism/naming.py: per-content-class filename templates,
  persona-conditioned. /var/log/cron.log + logrotate skeleton for
  system-class; /home/<persona>/TODO.md, scratch.md, etc. for
  user-class. Anti-regression test pins "no 8+ digit decimals in
  basenames" (the realism failure today).
- realism/bodies.py: deterministic body templates per content_class.
  TODO body uses checkbox markdown, script body has a shebang, cron
  body matches syslog cron shape ("CRON[PID]: (user) CMD (...)").
- realism/planner.py: pick(deckies, now, rng) returns a Plan.
  Diurnal-gated, weighted user/system content split (70/30 user
  bias). Create-only in stage 3; edit branch lands in stage 3b.

Scheduler split:

- scheduler.pick is now traffic-only (sync).
- scheduler.pick_file is async, takes a repo, resolves personas
  (Topology.email_personas for topology-source deckies; global
  realism.personas_pool otherwise), and maps Plan -> FileAction.
- FileAction gains persona/content_class/mtime fields.

Worker:

- _one_tick rolls 50/50 between traffic and file each tick. After a
  successful FileAction plant, _record_synthetic_file persists or
  patches the synthetic_files row (catching the unique-constraint
  collision on re-plant of the same path).
- SSHDriver._run_file passes action.mtime through to plant_file so
  files don't all stamp at wall-clock-now.

decnet/web/db/repository.py

@@ -1100,3 +1100,60 @@ class BaseRepository(ABC):
         this on a periodic tick.
         """
         raise NotImplementedError
+
+    # ------------------------------------------------------------- realism
+
+    async def record_synthetic_file(self, data: dict[str, Any]) -> str:
+        """Insert a new synthetic_files row, returning its uuid.
+
+        The ``(decky_uuid, path)`` pair has a UNIQUE constraint, so two
+        creates for the same target raise — callers either use this for
+        first-time plants and :meth:`update_synthetic_file` for edits,
+        or wrap in a transaction that catches the conflict.
+        """
+        raise NotImplementedError
+
+    async def update_synthetic_file(
+        self, uuid: str, data: dict[str, Any],
+    ) -> None:
+        """Patch an existing synthetic_files row.
+
+        Used by the realism edit-in-place flow (stage 3b): bumps
+        ``last_body``, ``content_hash``, ``last_modified``, and
+        ``edit_count``.  No-op when *uuid* doesn't exist (the row may
+        have been pruned between pick and apply).
+        """
+        raise NotImplementedError
+
+    async def list_synthetic_files(
+        self,
+        *,
+        decky_uuid: Optional[str] = None,
+        persona: Optional[str] = None,
+        limit: int = 100,
+        offset: int = 0,
+    ) -> list[dict[str, Any]]:
+        """Paginated synthetic_files newest-first.
+
+        Optional filters narrow to one decky and/or one persona, used by
+        the dashboard's "files this decky has grown" view.
+        """
+        raise NotImplementedError
+
+    async def pick_random_synthetic_file_for_edit(
+        self,
+        decky_uuid: str,
+        *,
+        max_age_days: int = 30,
+    ) -> Optional[dict[str, Any]]:
+        """Return a random eligible synthetic_files row for re-edit.
+
+        "Eligible" = belongs to *decky_uuid*, last_modified within
+        *max_age_days*, content_class supports body-level mutation
+        (``note``, ``todo``, ``draft``, ``script``, ``log_*``).
+        Returns ``None`` when nothing matches.
+
+        Used by the realism planner's ``action="edit"`` branch
+        (stage 3b).
+        """
+        raise NotImplementedError