fix(stage-1): audit High-severity backend correctness + CI unblocker

Closes 4 High-severity audit findings:

- describe_event broken for HTTP-async payloads: was reading source/op
  JSON fields that HttpDispatchPayload doesn't carry, producing empty
  source on DL rows. from_wire("") then fell back to Kv on replay, the
  dispatcher tried to resolve a non-existent trigger, and replay no-op'd
  silently. Now branches on OutboxSourceKind: HTTP rows emit
  "<method> <path>" + source="http"; Invoke rows emit "invoke_async" +
  source="invoke"; TriggerEvent payloads keep top-level field extraction.

- HTTP outbound Authorization leaked across cross-origin redirects.
  Manual redirect loop (Policy::none) reused header_map on every hop
  and only scrubbed Content-Type for POST->GET. Now compares
  url::Url::origin() across hops and strips Authorization,
  Proxy-Authorization, Cookie when origin changes — matching reqwest's
  default policy.

- F-S-010 inbound email HMAC had no replay protection. Signature was
  computed over body only with no timestamp or nonce, so captured POSTs
  were replayable indefinitely. Adds X-Picloud-Timestamp header bound
  into the HMAC input (signed string is ts || "." || body), 300s
  tolerance window, and a process-local LRU keyed on
  (ts, sha256(body)) with 600s TTL to catch within-window replays.
  Breaking change: webhook senders must include the timestamp header.

- expected_schema.txt re-blessed for migrations 0036-0039 (the previous
  snapshot stopped at 0035 so CI would have gone red on first run).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/picloud/src/lib.rs

@@ -18,19 +18,20 @@ use picloud_manager_core::{
     ApiKeyRepository, ApiKeysState, AppDomainRepository, AppMembersRepository, AppMembersState,
     AppRepository, AppsState, AuthState, AuthzRepo, DeadLetterRepo, DeadLettersState, Dispatcher,
     DocsServiceImpl, EmailInboundState, EmailServiceImpl, FilesAdminState, FilesConfig,
-    FilesServiceImpl, FsFilesRepo, HttpConfig, HttpServiceImpl, KvServiceImpl, OutboxEventEmitter,
-    OutboxRepo, PostgresAbandonedRepo, PostgresAdminSessionRepository, PostgresAdminUserRepository,
-    PostgresApiKeyRepository, PostgresAppDomainRepository, PostgresAppMembersRepository,
-    PostgresAppRepository, PostgresAppSecretsRepo, PostgresAppUserInvitationRepo,
-    PostgresAppUserPasswordResetRepo, PostgresAppUserRepository, PostgresAppUserRoleRepo,
-    PostgresAppUserSessionRepository, PostgresAppUserVerificationRepo, PostgresDeadLetterRepo,
-    PostgresDeadLetterService, PostgresDocsRepo, PostgresExecutionLogRepository,
-    PostgresExecutionLogSink, PostgresKvRepo, PostgresOutboxRepo, PostgresPubsubRepo,
-    PostgresRouteRepository, PostgresScriptRepository, PostgresSecretsRepo, PostgresTopicRepo,
-    PostgresTriggerRepo, PrincipalResolver, PubsubServiceImpl, RealtimeAuthorityImpl, RepoResolver,
-    RouteAdminState, RouteRepository, SandboxCeiling, ScriptRepository, SecretsConfig,
-    SecretsServiceImpl, SecretsState, SubscriberTokenConfig, TopicRepo, TopicsState, TriggerConfig,
-    TriggerRepo, TriggersState, UsersServiceConfig, UsersServiceImpl,
+    FilesServiceImpl, FsFilesRepo, HttpConfig, HttpServiceImpl, InboundNonceDedup, KvServiceImpl,
+    OutboxEventEmitter, OutboxRepo, PostgresAbandonedRepo, PostgresAdminSessionRepository,
+    PostgresAdminUserRepository, PostgresApiKeyRepository, PostgresAppDomainRepository,
+    PostgresAppMembersRepository, PostgresAppRepository, PostgresAppSecretsRepo,
+    PostgresAppUserInvitationRepo, PostgresAppUserPasswordResetRepo, PostgresAppUserRepository,
+    PostgresAppUserRoleRepo, PostgresAppUserSessionRepository, PostgresAppUserVerificationRepo,
+    PostgresDeadLetterRepo, PostgresDeadLetterService, PostgresDocsRepo,
+    PostgresExecutionLogRepository, PostgresExecutionLogSink, PostgresKvRepo, PostgresOutboxRepo,
+    PostgresPubsubRepo, PostgresRouteRepository, PostgresScriptRepository, PostgresSecretsRepo,
+    PostgresTopicRepo, PostgresTriggerRepo, PrincipalResolver, PubsubServiceImpl,
+    RealtimeAuthorityImpl, RepoResolver, RouteAdminState, RouteRepository, SandboxCeiling,
+    ScriptRepository, SecretsConfig, SecretsServiceImpl, SecretsState, SubscriberTokenConfig,
+    TopicRepo, TopicsState, TriggerConfig, TriggerRepo, TriggersState, UsersServiceConfig,
+    UsersServiceImpl,
 };
 use picloud_orchestrator_core::realtime::DEFAULT_GC_INTERVAL_SECS;
 use picloud_orchestrator_core::routing::{AppDomainTable, RouteTable};
@@ -453,6 +454,7 @@ pub async fn build_app(
         triggers: trigger_repo,
         outbox: outbox_repo.clone(),
         master_key: master_key.clone(),
+        nonce_dedup: Arc::new(InboundNonceDedup::new()),
     };
     let dead_letters_state = DeadLettersState {
         repo: dl_repo,