refactor(realism): move emailgen LLM/personas/prompt into shared library

Lift the format-agnostic pieces from decnet/orchestrator/emailgen/
into the new decnet/realism/ library so file-class content generation
(stage 3 of the realism migration) can reuse them. Email-specific
delivery (RFC 2822 EML, IMAP/POP3 spool, thread chains) stays in
orchestrator/.

Renames (history-preserving git mv):
  emailgen/personas.py     -> realism/personas.py
  emailgen/prompt.py       -> realism/prompts/email.py
  emailgen/global_pool.py  -> realism/personas_pool.py
  emailgen/llm/            -> realism/llm/

Env-var clean break (pre-v1, no aliases):
  DECNET_EMAILGEN_LLM      -> DECNET_REALISM_LLM
  DECNET_EMAILGEN_MODEL    -> DECNET_REALISM_MODEL
  DECNET_EMAILGEN_TIMEOUT  -> DECNET_REALISM_TIMEOUT
  DECNET_EMAILGEN_PERSONAS -> DECNET_REALISM_PERSONAS
  DECNET_EMAILGEN_FAKE_OUTPUT -> DECNET_REALISM_FAKE_OUTPUT

Importers rewritten in: orchestrator/emailgen/scheduler.py,
orchestrator/drivers/email.py, web/router/{emailgen,topology}/
api_personas.py, cli/emailgen.py. Tests for moved modules relocated
to tests/realism/; tests for stay-put modules updated in place.

API URL `/api/v1/emailgen/personas` and CLI `decnet emailgen
import-personas` keep their public names until the service-collapse
commit (stage 5).

tests/api/emailgen/test_personas_api.py

@@ -5,7 +5,7 @@ import json
 
 import pytest
 
-from decnet.orchestrator.emailgen import global_pool
+from decnet.realism import personas_pool as global_pool
 from decnet.web.router.emailgen.api_personas import (
     list_personas,
     replace_personas,
@@ -40,7 +40,7 @@ _VALID = [
 @pytest.mark.asyncio
 async def test_list_returns_empty_when_no_pool(tmp_path, monkeypatch):
     monkeypatch.setenv(
-        "DECNET_EMAILGEN_PERSONAS", str(tmp_path / "missing.json"),
+        "DECNET_REALISM_PERSONAS", str(tmp_path / "missing.json"),
     )
     result = await list_personas(user={"uuid": "u", "role": "viewer"})
     assert result["personas"] == []
@@ -51,7 +51,7 @@ async def test_list_returns_empty_when_no_pool(tmp_path, monkeypatch):
 async def test_list_returns_existing_pool(tmp_path, monkeypatch):
     pool = tmp_path / "pool.json"
     pool.write_text(json.dumps(_VALID))
-    monkeypatch.setenv("DECNET_EMAILGEN_PERSONAS", str(pool))
+    monkeypatch.setenv("DECNET_REALISM_PERSONAS", str(pool))
 
     result = await list_personas(user={"uuid": "u", "role": "viewer"})
     assert len(result["personas"]) == 2
@@ -63,7 +63,7 @@ async def test_list_returns_existing_pool(tmp_path, monkeypatch):
 @pytest.mark.asyncio
 async def test_replace_writes_canonical_file(tmp_path, monkeypatch):
     dest = tmp_path / "pool.json"
-    monkeypatch.setenv("DECNET_EMAILGEN_PERSONAS", str(dest))
+    monkeypatch.setenv("DECNET_REALISM_PERSONAS", str(dest))
 
     result = await replace_personas(
         body={"personas": _VALID},
@@ -83,7 +83,7 @@ async def test_replace_with_empty_list_clears_pool(tmp_path, monkeypatch):
     valid and means "no fleet personas, skip fleet mail deckies"."""
     dest = tmp_path / "pool.json"
     dest.write_text(json.dumps(_VALID))
-    monkeypatch.setenv("DECNET_EMAILGEN_PERSONAS", str(dest))
+    monkeypatch.setenv("DECNET_REALISM_PERSONAS", str(dest))
 
     result = await replace_personas(
         body={"personas": []},
@@ -98,7 +98,7 @@ async def test_replace_rejects_non_list_payload(tmp_path, monkeypatch):
     from fastapi import HTTPException
 
     monkeypatch.setenv(
-        "DECNET_EMAILGEN_PERSONAS", str(tmp_path / "pool.json"),
+        "DECNET_REALISM_PERSONAS", str(tmp_path / "pool.json"),
     )
     with pytest.raises(HTTPException) as exc:
         await replace_personas(
@@ -116,7 +116,7 @@ async def test_replace_rejects_all_invalid_payload(tmp_path, monkeypatch):
     from fastapi import HTTPException
 
     monkeypatch.setenv(
-        "DECNET_EMAILGEN_PERSONAS", str(tmp_path / "pool.json"),
+        "DECNET_REALISM_PERSONAS", str(tmp_path / "pool.json"),
     )
     with pytest.raises(HTTPException) as exc:
         await replace_personas(
@@ -132,7 +132,7 @@ async def test_replace_drops_partially_invalid_entries(tmp_path, monkeypatch):
     """One bad apple doesn't kill the request — invalid entries get
     dropped, valid ones land, response shows what stuck."""
     dest = tmp_path / "pool.json"
-    monkeypatch.setenv("DECNET_EMAILGEN_PERSONAS", str(dest))
+    monkeypatch.setenv("DECNET_REALISM_PERSONAS", str(dest))
 
     result = await replace_personas(
         body={"personas": [
@@ -153,7 +153,7 @@ async def test_get_then_put_round_trips_through_pool(tmp_path, monkeypatch):
     """The worker reads the same file the API writes — verify the
     write-then-read cycle leaves the pool in the expected state."""
     dest = tmp_path / "pool.json"
-    monkeypatch.setenv("DECNET_EMAILGEN_PERSONAS", str(dest))
+    monkeypatch.setenv("DECNET_REALISM_PERSONAS", str(dest))
 
     await replace_personas(
         body={"personas": _VALID},