Add PostgreSQL DurableStore substrate for WP-03

Introduce remora-durable with pool/migrations, a RemoraApiMutation-shaped
ledger, claim-fenced outbox projection, CAS helpers, and keyset cursors,
plus a kind Job acceptance suite against the hermetic fixture.

Cargo.toml

@@ -3,6 +3,7 @@ members = [
     "crates/remora-api",
     "crates/remora-contracts",
     "crates/remora-domain",
+    "crates/remora-durable",
     "crates/remora-worker",
 ]
 resolver = "3"
@@ -13,11 +14,24 @@ rust-version = "1.97"
 version = "0.0.0"
 
 [workspace.dependencies]
+base64 = "0.22.1"
+hmac = "0.13.0"
 remora-domain = { path = "crates/remora-domain" }
 serde = { version = "1.0.228", features = ["derive"] }
 serde_json = "1.0.150"
 serde_json_canonicalizer = "0.3.2"
 sha2 = "0.11.0"
-time = { version = "0.3.47", features = ["parsing"] }
+sqlx = { version = "0.9.0", default-features = false, features = [
+    "json",
+    "macros",
+    "migrate",
+    "postgres",
+    "runtime-tokio",
+    "time",
+    "tls-rustls-ring-webpki",
+] }
+thiserror = "2.0.17"
+time = { version = "0.3.47", features = ["formatting", "macros", "parsing", "serde"] }
+tokio = { version = "1.52.3", features = ["macros", "rt-multi-thread", "sync", "time"] }
 unicode-general-category = "1.1.0"
 unicode-normalization = "0.1.25"