feat(backend): bootstrap Go module, config, and data plane

Introduce configuration validation, Postgres migrations, Redis/storage adapters, and the seed sample video.

backend/internal/db/migrations/0009_identity_cert.sql

@@ -0,0 +1,54 @@
+-- Identity, Telegram, security Q/A, certificates, physical orders
+
+ALTER TABLE users ADD COLUMN IF NOT EXISTS phone TEXT NOT NULL DEFAULT '';
+ALTER TABLE users ADD COLUMN IF NOT EXISTS telegram_id BIGINT;
+ALTER TABLE users ADD COLUMN IF NOT EXISTS telegram_username TEXT NOT NULL DEFAULT '';
+ALTER TABLE users ADD COLUMN IF NOT EXISTS security_question TEXT NOT NULL DEFAULT '';
+ALTER TABLE users ADD COLUMN IF NOT EXISTS security_answer_hash TEXT NOT NULL DEFAULT '';
+
+CREATE UNIQUE INDEX IF NOT EXISTS users_phone_uidx
+    ON users (phone) WHERE phone <> '';
+
+CREATE UNIQUE INDEX IF NOT EXISTS users_telegram_id_uidx
+    ON users (telegram_id) WHERE telegram_id IS NOT NULL;
+
+CREATE TABLE IF NOT EXISTS certificates (
+    id          BIGSERIAL PRIMARY KEY,
+    user_id     BIGINT NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    public_id   TEXT NOT NULL UNIQUE,
+    full_name   TEXT NOT NULL,
+    issued_at   TIMESTAMPTZ NOT NULL DEFAULT now(),
+    revoked_at  TIMESTAMPTZ,
+    UNIQUE (user_id)
+);
+
+CREATE INDEX IF NOT EXISTS certificates_public_id_idx ON certificates (public_id);
+
+CREATE TYPE physical_order_status AS ENUM ('requested', 'paid', 'shipped', 'cancelled');
+
+CREATE TABLE IF NOT EXISTS certificate_physical_orders (
+    id              BIGSERIAL PRIMARY KEY,
+    certificate_id  BIGINT NOT NULL REFERENCES certificates(id) ON DELETE CASCADE,
+    user_id         BIGINT NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    status          physical_order_status NOT NULL DEFAULT 'requested',
+    note            TEXT NOT NULL DEFAULT '',
+    window_ends_at  TIMESTAMPTZ NOT NULL,
+    created_at      TIMESTAMPTZ NOT NULL DEFAULT now(),
+    updated_at      TIMESTAMPTZ NOT NULL DEFAULT now()
+);
+
+CREATE INDEX IF NOT EXISTS cert_physical_orders_user_idx
+    ON certificate_physical_orders (user_id, created_at DESC);
+CREATE INDEX IF NOT EXISTS cert_physical_orders_status_idx
+    ON certificate_physical_orders (status, created_at DESC);
+
+CREATE TABLE IF NOT EXISTS app_settings (
+    key   TEXT PRIMARY KEY,
+    value TEXT NOT NULL DEFAULT ''
+);
+
+INSERT INTO app_settings (key, value) VALUES
+    ('physical_cert_enabled', 'true'),
+    ('physical_cert_price_irr', '2500000'),
+    ('physical_cert_window_days', '30')
+ON CONFLICT (key) DO NOTHING;