P0: workspace scaffold, CI gates, tc-domain, tc-config, tc-db vs real Postgres

- Cargo workspace with 1250-line and no-placeholder CI gates wired first
- tc-domain: id newtypes, SessionKey codec (proptest round-trip), Role,
  GatedCategory (spec §15), AccessPolicy, core entities
- tc-config: figment TOML+env config, DeployTarget/provider/auth selection
  with semantic validation
- migrations/0001: full spec §14 schema incl. DB-enforced append-only audit_log
- tc-db: compile-time-checked sqlx repos (workspaces, users, agents+policies,
  credits, audit) with committed .sqlx offline metadata
- tc-testkit: per-test real-Postgres databases (testcontainers or
  TC_TEST_DATABASE_URL), embedded migrations

Co-Authored-By: Claude Fable 5 <[email protected]>

crates/tc-domain/src/role.rs

@@ -0,0 +1,16 @@
+use serde::{Deserialize, Serialize};
+
+/// Workspace-level RBAC role (spec §14: User.role Owner|Member).
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[serde(rename_all = "lowercase")]
+pub enum Role {
+    Owner,
+    Member,
+}
+
+impl Role {
+    /// Owners administer provisioning, billing, and access policy (spec §1).
+    pub fn is_owner(&self) -> bool {
+        matches!(self, Role::Owner)
+    }
+}