Add PostgreSQL schema and migration runner

All tables per PRD data model with default config seeds.
Migration runner tracks applied migrations in DB.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

db/migrations/001_initial_schema.sql

@@ -0,0 +1,92 @@
+-- App configuration (key/value store)
+CREATE TABLE IF NOT EXISTS config (
+  key   TEXT PRIMARY KEY,
+  value TEXT NOT NULL
+);
+
+-- Seed default config
+INSERT INTO config (key, value) VALUES
+  ('paycheck1_day', '1'),
+  ('paycheck2_day', '15'),
+  ('paycheck1_gross', '0'),
+  ('paycheck1_net', '0'),
+  ('paycheck2_gross', '0'),
+  ('paycheck2_net', '0')
+ON CONFLICT (key) DO NOTHING;
+
+-- Bill definitions
+CREATE TABLE IF NOT EXISTS bills (
+  id               SERIAL PRIMARY KEY,
+  name             TEXT NOT NULL,
+  amount           NUMERIC(10,2) NOT NULL,
+  due_day          INTEGER NOT NULL CHECK (due_day BETWEEN 1 AND 31),
+  assigned_paycheck INTEGER NOT NULL CHECK (assigned_paycheck IN (1, 2)),
+  category         TEXT NOT NULL DEFAULT 'General',
+  active           BOOLEAN NOT NULL DEFAULT TRUE,
+  created_at       TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+-- Paycheck instances per period
+CREATE TABLE IF NOT EXISTS paychecks (
+  id               SERIAL PRIMARY KEY,
+  period_year      INTEGER NOT NULL,
+  period_month     INTEGER NOT NULL CHECK (period_month BETWEEN 1 AND 12),
+  paycheck_number  INTEGER NOT NULL CHECK (paycheck_number IN (1, 2)),
+  pay_date         DATE NOT NULL,
+  gross            NUMERIC(10,2) NOT NULL DEFAULT 0,
+  net              NUMERIC(10,2) NOT NULL DEFAULT 0,
+  UNIQUE (period_year, period_month, paycheck_number)
+);
+
+-- Bills assigned to a paycheck period
+CREATE TABLE IF NOT EXISTS paycheck_bills (
+  id              SERIAL PRIMARY KEY,
+  paycheck_id     INTEGER NOT NULL REFERENCES paychecks(id) ON DELETE CASCADE,
+  bill_id         INTEGER NOT NULL REFERENCES bills(id) ON DELETE CASCADE,
+  amount_override NUMERIC(10,2),
+  paid            BOOLEAN NOT NULL DEFAULT FALSE,
+  paid_at         TIMESTAMPTZ,
+  UNIQUE (paycheck_id, bill_id)
+);
+
+-- Savings goals
+CREATE TABLE IF NOT EXISTS savings_goals (
+  id                SERIAL PRIMARY KEY,
+  name              TEXT NOT NULL,
+  amount            NUMERIC(10,2) NOT NULL,
+  assigned_paycheck INTEGER NOT NULL CHECK (assigned_paycheck IN (1, 2)),
+  active            BOOLEAN NOT NULL DEFAULT TRUE
+);
+
+-- One-time expenses
+CREATE TABLE IF NOT EXISTS one_time_expenses (
+  id          SERIAL PRIMARY KEY,
+  paycheck_id INTEGER NOT NULL REFERENCES paychecks(id) ON DELETE CASCADE,
+  name        TEXT NOT NULL,
+  amount      NUMERIC(10,2) NOT NULL,
+  paid        BOOLEAN NOT NULL DEFAULT FALSE,
+  paid_at     TIMESTAMPTZ
+);
+
+-- Variable expense categories
+CREATE TABLE IF NOT EXISTS expense_categories (
+  id   SERIAL PRIMARY KEY,
+  name TEXT NOT NULL UNIQUE
+);
+
+-- Seed default categories
+INSERT INTO expense_categories (name) VALUES
+  ('Groceries'), ('Gas'), ('Dining'), ('Entertainment'), ('Medical'), ('Other')
+ON CONFLICT (name) DO NOTHING;
+
+-- Actual spending log
+CREATE TABLE IF NOT EXISTS actuals (
+  id          SERIAL PRIMARY KEY,
+  paycheck_id INTEGER NOT NULL REFERENCES paychecks(id) ON DELETE CASCADE,
+  category_id INTEGER REFERENCES expense_categories(id),
+  bill_id     INTEGER REFERENCES bills(id),
+  amount      NUMERIC(10,2) NOT NULL,
+  note        TEXT,
+  date        DATE NOT NULL DEFAULT CURRENT_DATE,
+  created_at  TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);