feat: Add working hours for natural traffic patterns

Workers check their timezone (from preflight IP geolocation) and current
hour's weight probability to determine availability. This creates natural
traffic patterns - more workers active during peak hours, fewer during
off-peak. Tasks queue up at night and drain during the day.

Migrations:
- 099: working_hours table with hourly weights by profile
- 100: Add timezone column to worker_registry
- 101: Store timezone from preflight IP geolocation
- 102: check_working_hours() function with probability roll

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/migrations/102_check_working_hours.sql

@@ -0,0 +1,114 @@
+-- Migration: 102_check_working_hours.sql
+-- Description: Function to check if worker should be available based on working hours
+-- Created: 2024-12-13
+
+-- Function to check if a worker should be available for work
+-- Returns TRUE if worker passes the probability check for current hour
+-- Returns FALSE if worker should sleep/skip this cycle
+CREATE OR REPLACE FUNCTION check_working_hours(
+  p_worker_id VARCHAR,
+  p_profile_name VARCHAR DEFAULT 'natural_traffic'
+)
+RETURNS TABLE (
+  is_available BOOLEAN,
+  current_hour INTEGER,
+  hour_weight INTEGER,
+  worker_timezone VARCHAR,
+  roll INTEGER,
+  reason TEXT
+)
+LANGUAGE plpgsql
+AS $function$
+DECLARE
+  v_timezone VARCHAR(50);
+  v_hour INTEGER;
+  v_weight INTEGER;
+  v_dow INTEGER;
+  v_dow_weight INTEGER;
+  v_final_weight INTEGER;
+  v_roll INTEGER;
+  v_hour_weights JSONB;
+  v_dow_weights JSONB;
+  v_profile_enabled BOOLEAN;
+BEGIN
+  -- Get worker's timezone (from preflight)
+  SELECT wr.timezone INTO v_timezone
+  FROM worker_registry wr
+  WHERE wr.worker_id = p_worker_id;
+
+  -- Default to America/Phoenix if no timezone set
+  v_timezone := COALESCE(v_timezone, 'America/Phoenix');
+
+  -- Get current hour in worker's timezone
+  v_hour := EXTRACT(HOUR FROM NOW() AT TIME ZONE v_timezone)::INTEGER;
+
+  -- Get day of week (0=Sunday)
+  v_dow := EXTRACT(DOW FROM NOW() AT TIME ZONE v_timezone)::INTEGER;
+
+  -- Get working hours profile
+  SELECT wh.hour_weights, wh.dow_weights, wh.enabled
+  INTO v_hour_weights, v_dow_weights, v_profile_enabled
+  FROM working_hours wh
+  WHERE wh.name = p_profile_name AND wh.enabled = true;
+
+  -- If profile not found or disabled, always available
+  IF v_hour_weights IS NULL THEN
+    RETURN QUERY SELECT
+      TRUE::BOOLEAN,
+      v_hour,
+      100::INTEGER,
+      v_timezone,
+      0::INTEGER,
+      'Profile not found or disabled - defaulting to available'::TEXT;
+    RETURN;
+  END IF;
+
+  -- Get hour weight (default to 50 if hour not specified)
+  v_weight := COALESCE((v_hour_weights->>v_hour::TEXT)::INTEGER, 50);
+
+  -- Get day-of-week weight (default to 100)
+  v_dow_weight := COALESCE((v_dow_weights->>v_dow::TEXT)::INTEGER, 100);
+
+  -- Calculate final weight (hour_weight * dow_weight / 100)
+  v_final_weight := (v_weight * v_dow_weight / 100);
+
+  -- Roll the dice (0-99)
+  v_roll := floor(random() * 100)::INTEGER;
+
+  -- Return result
+  RETURN QUERY SELECT
+    (v_roll < v_final_weight)::BOOLEAN AS is_available,
+    v_hour AS current_hour,
+    v_final_weight AS hour_weight,
+    v_timezone AS worker_timezone,
+    v_roll AS roll,
+    CASE
+      WHEN v_roll < v_final_weight THEN
+        format('Available: rolled %s < %s%% threshold', v_roll, v_final_weight)
+      ELSE
+        format('Sleeping: rolled %s >= %s%% threshold', v_roll, v_final_weight)
+    END AS reason;
+END;
+$function$;
+
+-- Simplified version that just returns boolean
+CREATE OR REPLACE FUNCTION is_worker_available(
+  p_worker_id VARCHAR,
+  p_profile_name VARCHAR DEFAULT 'natural_traffic'
+)
+RETURNS BOOLEAN
+LANGUAGE plpgsql
+AS $function$
+DECLARE
+  v_result BOOLEAN;
+BEGIN
+  SELECT is_available INTO v_result
+  FROM check_working_hours(p_worker_id, p_profile_name);
+  RETURN COALESCE(v_result, TRUE);
+END;
+$function$;
+
+COMMENT ON FUNCTION check_working_hours(VARCHAR, VARCHAR) IS
+  'Check if worker should be available based on working hours profile. Returns detailed info.';
+COMMENT ON FUNCTION is_worker_available(VARCHAR, VARCHAR) IS
+  'Simple boolean check if worker passes working hours probability roll.';