feat(webapp): default tx-start retry to 3 attempts (2 retries)

A 20-25s PlanetScale reader freeze can outlast 2 attempts (~2x maxWait ~= 20s tolerance).
3 attempts (~30s) covers it. Verified on the pooler-freeze rig: a 25s freeze loses 7/12 tx-starts
at maxAttempts=2 but 12/12 survive at 3.

Author: ericallam

apps/webapp/app/env.server.ts

@@ -157,7 +157,7 @@ const EnvironmentSchema = z
     DATABASE_READ_REPLICA_CONNECTION_TIMEOUT: OptionalIntEnv,
     DATABASE_TRANSACTION_MAX_WAIT_MS: IntEnvWithDefault(10000),
     DATABASE_TRANSACTION_START_RETRY_ENABLED: BoolEnv.default(true),
-    DATABASE_TRANSACTION_START_RETRY_MAX_ATTEMPTS: IntEnvWithDefault(2),
+    DATABASE_TRANSACTION_START_RETRY_MAX_ATTEMPTS: IntEnvWithDefault(3),
     DATABASE_TRANSACTION_START_RETRY_BACKOFF_MIN_MS: IntEnvWithDefault(50),
     DATABASE_TRANSACTION_START_RETRY_BACKOFF_MAX_MS: IntEnvWithDefault(250),
     DATABASE_TRANSACTION_START_RETRY_BUDGET_PER_SEC: IntEnvWithDefault(50),