Add authentication, authorization, and team-scoped access control

Implement email/password auth with JWT sessions and API key auth for
sandbox lifecycle. Users get a default team on signup; sandboxes,
snapshots, and API keys are scoped to teams.

- Add user, team, users_teams, and team_api_keys tables (goose migrations)
- Add JWT middleware (Bearer token) for user management endpoints
- Add API key middleware (X-API-Key header, SHA-256 hashed) for sandbox ops
- Add signup/login handlers with transactional user+team creation
- Add API key CRUD endpoints (create/list/delete)
- Replace owner_id with team_id on sandboxes and templates
- Update all handlers to use team-scoped queries
- Add godotenv for .env file loading
- Update OpenAPI spec and test UI with auth flows

db/migrations/20260313210608_auth.sql

@@ -0,0 +1,46 @@
+-- +goose Up
+
+CREATE TABLE users (
+    id            TEXT PRIMARY KEY,
+    email         TEXT NOT NULL UNIQUE,
+    password_hash TEXT NOT NULL,
+    created_at    TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    updated_at    TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+CREATE TABLE teams (
+    id         TEXT PRIMARY KEY,
+    name       TEXT NOT NULL,
+    created_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+CREATE TABLE users_teams (
+    user_id    TEXT NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    team_id    TEXT NOT NULL REFERENCES teams(id) ON DELETE CASCADE,
+    is_default BOOLEAN NOT NULL DEFAULT TRUE,
+    role       TEXT NOT NULL DEFAULT 'owner',
+    created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    PRIMARY KEY (team_id, user_id)
+);
+
+CREATE INDEX idx_users_teams_user ON users_teams(user_id);
+
+CREATE TABLE team_api_keys (
+    id         TEXT PRIMARY KEY,
+    team_id    TEXT NOT NULL REFERENCES teams(id) ON DELETE CASCADE,
+    name       TEXT NOT NULL DEFAULT '',
+    key_hash   TEXT NOT NULL UNIQUE,
+    key_prefix TEXT NOT NULL DEFAULT '',
+    created_by TEXT NOT NULL REFERENCES users(id),
+    created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    last_used  TIMESTAMPTZ
+);
+
+CREATE INDEX idx_team_api_keys_team ON team_api_keys(team_id);
+
+-- +goose Down
+
+DROP TABLE team_api_keys;
+DROP TABLE users_teams;
+DROP TABLE teams;
+DROP TABLE users;

db/migrations/20260313210611_team_ownership.sql

@@ -0,0 +1,31 @@
+-- +goose Up
+
+ALTER TABLE sandboxes
+    ADD COLUMN team_id TEXT NOT NULL DEFAULT '';
+
+UPDATE sandboxes SET team_id = owner_id WHERE owner_id != '';
+
+ALTER TABLE sandboxes
+    DROP COLUMN owner_id;
+
+ALTER TABLE templates
+    ADD COLUMN team_id TEXT NOT NULL DEFAULT '';
+
+CREATE INDEX idx_sandboxes_team ON sandboxes(team_id);
+CREATE INDEX idx_templates_team ON templates(team_id);
+
+-- +goose Down
+
+ALTER TABLE sandboxes
+    ADD COLUMN owner_id TEXT NOT NULL DEFAULT '';
+
+UPDATE sandboxes SET owner_id = team_id WHERE team_id != '';
+
+ALTER TABLE sandboxes
+    DROP COLUMN team_id;
+
+ALTER TABLE templates
+    DROP COLUMN team_id;
+
+DROP INDEX IF EXISTS idx_sandboxes_team;
+DROP INDEX IF EXISTS idx_templates_team;