Add FMCSA motor carrier census table and Socrata data downloader

New vertical: FMCSA/DOT motor carrier compliance services.
- Migration 078: fmcsa_carriers table with 31 fields (DOT#, name,
  email, phone, address, fleet size, MCS-150 date, carrier type)
- Downloader: Socrata API ingest for 2M+ carriers with upsert
- Data source: data.transportation.gov (free, public)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

api/migrations/078_fmcsa_carriers.sql

@@ -0,0 +1,57 @@
+-- FMCSA Motor Carrier Census Data
+CREATE TABLE IF NOT EXISTS fmcsa_carriers (
+    id SERIAL PRIMARY KEY,
+    dot_number TEXT NOT NULL UNIQUE,
+    legal_name TEXT NOT NULL,
+    dba_name TEXT,
+    carrier_operation TEXT,       -- C=carrier, B=broker, etc.
+    authorized_for_hire BOOLEAN DEFAULT FALSE,
+    private_property BOOLEAN DEFAULT FALSE,
+    private_passenger_business BOOLEAN DEFAULT FALSE,
+    exempt_for_hire BOOLEAN DEFAULT FALSE,
+    hm_flag BOOLEAN DEFAULT FALSE,
+    
+    -- Contact
+    email_address TEXT,
+    telephone TEXT,
+    
+    -- Physical address
+    phy_street TEXT,
+    phy_city TEXT,
+    phy_state TEXT,
+    phy_zip TEXT,
+    phy_country TEXT,
+    
+    -- Mailing address
+    mailing_street TEXT,
+    mailing_city TEXT,
+    mailing_state TEXT,
+    mailing_zip TEXT,
+    mailing_country TEXT,
+    
+    -- Fleet info
+    nbr_power_unit INTEGER,
+    driver_total INTEGER,
+    mcs150_mileage INTEGER,
+    mcs150_mileage_year INTEGER,
+    recent_mileage INTEGER,
+    recent_mileage_year INTEGER,
+    
+    -- Compliance dates
+    mcs150_date TEXT,              -- raw date string from FMCSA
+    mcs150_parsed DATE,            -- parsed for querying
+    add_date TEXT,                 -- registration date
+    
+    -- State info
+    oic_state TEXT,                -- state of principal office
+    
+    -- Metadata
+    created_at TIMESTAMPTZ DEFAULT NOW(),
+    updated_at TIMESTAMPTZ DEFAULT NOW()
+);
+
+CREATE INDEX IF NOT EXISTS idx_fmcsa_dot ON fmcsa_carriers(dot_number);
+CREATE INDEX IF NOT EXISTS idx_fmcsa_email ON fmcsa_carriers(email_address) WHERE email_address IS NOT NULL;
+CREATE INDEX IF NOT EXISTS idx_fmcsa_state ON fmcsa_carriers(phy_state);
+CREATE INDEX IF NOT EXISTS idx_fmcsa_mcs150 ON fmcsa_carriers(mcs150_parsed);
+CREATE INDEX IF NOT EXISTS idx_fmcsa_hire ON fmcsa_carriers(authorized_for_hire) WHERE authorized_for_hire = TRUE;