feat(monitoring): bot observability dashboards — Grafana + Persian RTL ERP page

Grafana (full use of the existing monitoring/ stack, per OSS policy):
- datasources.yml: BotPostgres (uid bot-postgres) over the shared network;
  grafana service joins 'shared' + carries the datasource env
- db_init.py: idempotent read-only role obs_reader (USAGE on schema public +
  SELECT on bot_traces/bot_trace_events; skipped when
  OBS_READER_PASSWORD empty; ALTER ROLE for rotation) + composite index
  ix_bot_trace_events_stage_time (stage, created_at DESC) — senior-engineer
  review applied with the column-name fix (event_type -> stage); (trace_id)
  already covered by the existing (trace_id, created_at) index
- dashboards/bot-observability.json: KPI row (real traffic, events, Jev/
  fallback errors, Jev p95, tokens, commits, archive guard), events/day,
  per-stage p50/p95, mention statuses (arbiter+fallback aggregates + legacy
  rows), DeepSeek arbiter actions, tokens/day, model-drift vs jev-1.13.0,
  user-choice A/B, STT + audio.enhance health, archive size guard
- dashboards/bot-trace-explorer.json: trace table + full event drill-down
  via the trace_id variable

ERP page (admin-only, Persian RTL, recharts@^3 for React 19):
- backend bot_metrics.py: read-only require_role('admin') endpoints
  (summary/routing/quality/jev/stt/traces + trace detail); aggregates count
  real traffic only (calibration/demo/chat_id=0 excluded)
- frontend BotMonitorPage at /bot-monitor (KPI cards, daily events,
  status donut, arbiter actions, user-choice A/B, STT/enhance tables,
  stage latency, tokens chart, traces table + detail drawer with payload
  viewer); entry link from the admin panel; MobileTabBar hidden there
- api.ts: typed botMetrics client section

Tooling/docs:
- tools/seed_observability_demo.py: deterministic demo traces (source='demo',
  every current pipeline stage incl. audio.enhance/jev.failure/arbitration/
  fallback/user choices) — excluded from real-traffic aggregates
- monitoring/README.md + bot/docs/DEPLOY-AND-MONITORING.md: setup, seed and
  rollback notes; alerts deliberately deferred (owner decision 2026-10-24)

Verified locally: obs_reader SELECT ok / INSERT denied; panels' SQL run as
obs_reader with data; datasource health OK; both dashboards survive a grafana
restart; endpoints 200 as admin and 403 without role; tsc + vite build clean;
page renders in-browser (admin session); bot startup provisions role+index.

bot/app/config.py

@@ -147,6 +147,10 @@ class Settings(BaseSettings):
     OBS_ENABLED: bool = True
     OBS_VOICE_DIR: str = "data/voices"   # persistent volume (./bot/data) — keep forever
     OBS_PROMPT_VERSION: str = ""         # manual label for the NLU prompt in use
+    # Read-only DB role for the Grafana datasource (dashboard phase 1); empty =
+    # role provisioning is skipped (local dev can point the datasource at the
+    # postgres user instead). Rotating = change env + restart the bot.
+    OBS_READER_PASSWORD: str = ""
 
     # Jev (TypeSafe) entity matching — phases 2-5. Model version is PINNED
     # (phase 0 resolved jev-1.13.0) so upstream updates cannot silently change