Add multi-user auth, admin panel, and timezone support; rename to Yolkbook

- Rename app from Eggtracker to Yolkbook throughout
- Add JWT-based authentication (python-jose, passlib/bcrypt)
- Add users table; all data tables gain user_id FK for full data isolation
- Super admin credentials sourced from ADMIN_USERNAME/ADMIN_PASSWORD env vars,
  synced on every startup; orphaned rows auto-assigned to admin post-migration
- Login page with self-registration; JWT stored in localStorage (30-day expiry)
- Admin panel (/admin): list users, reset passwords, disable/enable, delete,
  and impersonate (Login As) with Return to Admin banner
- Settings modal (gear icon in nav): timezone selector and change password
- Timezone stored per-user; stats date windows computed in user's timezone;
  date input setToday() respects user timezone via Intl API
- migrate_v2.sql for existing single-user installs
- Auto-migration adds timezone column to users on startup
- Updated README with full setup, auth, admin, and migration docs

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

mysql/migrate_v2.sql

@@ -0,0 +1,50 @@
+-- Eggtracker v2 migration — adds multi-user support to an existing database.
+-- Run this ONCE on an existing install BEFORE restarting with the new image:
+--
+--   docker compose exec db mysql -u root -p"${MYSQL_ROOT_PASSWORD}" eggtracker < mysql/migrate_v2.sql
+--
+-- After running this script, restart the stack (docker compose up -d --build).
+-- The API will automatically create the admin user (from ADMIN_USERNAME /
+-- ADMIN_PASSWORD in .env) and assign all existing records to that admin account.
+--
+-- NOTE: Run this script only ONCE. Running it again will fail on the ADD COLUMN
+-- statements since the columns will already exist.
+
+USE eggtracker;
+
+-- ── Create users table ────────────────────────────────────────────────────────
+CREATE TABLE IF NOT EXISTS users (
+    id              INT UNSIGNED    NOT NULL AUTO_INCREMENT,
+    username        VARCHAR(64)     NOT NULL,
+    hashed_password VARCHAR(255)    NOT NULL,
+    is_admin        TINYINT(1)      NOT NULL DEFAULT 0,
+    is_disabled     TINYINT(1)      NOT NULL DEFAULT 0,
+    created_at      DATETIME        NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    PRIMARY KEY (id),
+    UNIQUE KEY uq_username (username)
+) ENGINE=InnoDB;
+
+-- ── Add user_id columns (nullable so existing rows remain valid) ───────────────
+ALTER TABLE egg_collections
+    ADD COLUMN user_id INT UNSIGNED NULL AFTER id,
+    ADD INDEX idx_user_id (user_id);
+
+ALTER TABLE flock_history
+    ADD COLUMN user_id INT UNSIGNED NULL AFTER id,
+    ADD INDEX idx_user_id (user_id);
+
+ALTER TABLE feed_purchases
+    ADD COLUMN user_id INT UNSIGNED NULL AFTER id,
+    ADD INDEX idx_user_id (user_id);
+
+ALTER TABLE other_purchases
+    ADD COLUMN user_id INT UNSIGNED NULL AFTER id,
+    ADD INDEX idx_user_id (user_id);
+
+-- ── Remove old single-column unique index on egg_collections.date ─────────────
+-- It will be replaced by (user_id, date) once the admin is seeded.
+ALTER TABLE egg_collections DROP INDEX uq_date;
+
+-- The API startup will:
+-- 1. Create the admin user from ADMIN_USERNAME / ADMIN_PASSWORD in .env
+-- 2. Set user_id = admin.id on all rows where user_id IS NULL