fix(whatsapp,roles): self-heal legacy whatsapp_log schema; map underscore role aliases

CT115 (Mumuni relay #747) — two live-instance defects after PR #12:

1. GET /api/whatsapp/mock-log 500'd with a valid admin token:
   'no such column: whatsapp_log.message_text'. The model gained
   message_text/wa_message_id/ticket_number (and dropped command) in
   4afdc36 with no migration, so legacy DBs keep the (command, ...) shape.
   ensure_legacy_schema (startup, app/main.py) now adds the three missing
   columns idempotently and backfills legacy command bodies into
   message_text before dropping the obsolete NOT NULL command column, so
   both the mock-log read path and the ORM write path work on healed DBs.
   New producer/consumer regression (tests/test_whatsapp_log_legacy_heal.py)
   reproduces the exact OperationalError, then asserts 200 + data.

2. ROLE_ALIASES gap: underscore legacy roles (cs_rep, cs_manager,
   fm_dispatcher) were not mapped, so normalize_legacy_user_roles could not
   converge rows like user 18 (test@denya.com, role 'cs_rep') and the
   frontend stranded them on /tickets. Added the underscore aliases; tests
   assert normalize_role('cs_rep') == 'CS Rep' and a cs_rep row converges
   and authenticates.

app/core/roles.py

@@ -12,8 +12,9 @@ uses (PRD §4, ``app/services/seed.py``, the frontend nav in base.html):
 
 Legacy databases created under the pre-P0 open-registration builds can carry
 lowercase/nickname role strings (``technician``, ``cs``, ``fm``, ``ceo``,
-``admin``, ``superadmin`` …).  ``ROLE_ALIASES`` maps the *unambiguous*
-nicknames onto a canonical role so startup normalization (see
+``admin``, ``superadmin`` …) and underscore variants of the space-separated
+ones (``cs_rep``, ``cs_manager``, ``fm_dispatcher``).  ``ROLE_ALIASES`` maps
+the *unambiguous* nicknames onto a canonical role so startup normalization (see
 ``app/services/seed.py::normalize_legacy_user_roles``) can converge the data.
 
 ``admin`` / ``superadmin`` are deliberately NOT aliased: they are
@@ -52,10 +53,13 @@ ROLE_ALIASES: dict[str, str] = {
     "tech": TECHNICIAN_ROLE,
     "cs": "CS Rep",
     "cs rep": "CS Rep",
+    "cs_rep": "CS Rep",
     "cs representative": "CS Rep",
     "cs manager": "CS Manager",
+    "cs_manager": "CS Manager",
     "fm": "FM Dispatcher",
     "fm dispatcher": "FM Dispatcher",
+    "fm_dispatcher": "FM Dispatcher",
     "ceo": "CEO",
     "director": "Director",
 }