feat(vars): VarsService + vars:: SDK + config capabilities

Scripts can now read group-inherited config via vars::get(key) / vars::all().

- shared: VarsService trait (read-only get/all) + NoopVarsService; added as
  the 14th field on the Services bundle.
- manager-core: VarsServiceImpl resolves the calling app's config via
  config_resolver (derives app_id from cx.app_id; AppVarsRead-gated for
  authed principals, script-as-gate for anon).
- executor-core: vars:: Rhai bridge (get/all), registered in the SDK.
- authz: AppVarsRead/Write, GroupVarsRead/Write, GroupSecretsRead/Write
  capabilities (group caps resolve via the Phase-2 ancestor walk; the
  GroupSecretsRead human-read gate is group_admin-only, distinct from an
  app's runtime injection).
- wired VarsServiceImpl into the picloud binary; updated the executor-core
  test Services::new call sites.

386 manager-core lib tests green; clippy clean.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/manager-core/src/vars_service.rs

@@ -0,0 +1,63 @@
+//! `VarsService` — the runtime read path for group-inherited config.
+//!
+//! Resolves the calling app's config (own rows + inherited group rows,
+//! env-filtered, proximity-first; see `config_resolver`) and exposes it to
+//! scripts as `vars::get(key)` / `vars::all()`. Read-only from scripts;
+//! writes go through the admin API. Like every SDK service, it derives the
+//! app from `cx.app_id` — never a script argument — so cross-app isolation
+//! holds.
+
+use std::collections::BTreeMap;
+use std::sync::Arc;
+
+use async_trait::async_trait;
+use picloud_shared::{SdkCallCx, VarsError, VarsService};
+use serde_json::Value;
+use sqlx::PgPool;
+
+use crate::authz::{self, AuthzRepo, Capability};
+use crate::config_resolver::{fetch_var_candidates, resolve};
+
+pub struct VarsServiceImpl {
+    pool: PgPool,
+    authz: Arc<dyn AuthzRepo>,
+}
+
+impl VarsServiceImpl {
+    #[must_use]
+    pub fn new(pool: PgPool, authz: Arc<dyn AuthzRepo>) -> Self {
+        Self { pool, authz }
+    }
+
+    /// Authed principals need `AppVarsRead`; anonymous public-HTTP scripts
+    /// (`principal: None`) read freely under script-as-gate semantics.
+    async fn check_read(&self, cx: &SdkCallCx) -> Result<(), VarsError> {
+        if let Some(ref principal) = cx.principal {
+            authz::require(&*self.authz, principal, Capability::AppVarsRead(cx.app_id))
+                .await
+                .map_err(|_| VarsError::Forbidden)?;
+        }
+        Ok(())
+    }
+
+    async fn resolved(&self, cx: &SdkCallCx) -> Result<BTreeMap<String, Value>, VarsError> {
+        let candidates = fetch_var_candidates(&self.pool, cx.app_id)
+            .await
+            .map_err(|e| VarsError::Backend(e.to_string()))?;
+        let (values, _provenance) = resolve(candidates);
+        Ok(values)
+    }
+}
+
+#[async_trait]
+impl VarsService for VarsServiceImpl {
+    async fn get(&self, cx: &SdkCallCx, key: &str) -> Result<Option<Value>, VarsError> {
+        self.check_read(cx).await?;
+        Ok(self.resolved(cx).await?.remove(key))
+    }
+
+    async fn all(&self, cx: &SdkCallCx) -> Result<BTreeMap<String, Value>, VarsError> {
+        self.check_read(cx).await?;
+        self.resolved(cx).await
+    }
+}