feat(cli): collections manifest + ls + journeys; rename to kv::shared_collection (§11.6 C5)

Finish the §11.6 KV slice: declarative authoring, read-only inspection, the
runtime journey, and docs — plus a forced SDK-name fix.

- SDK name: `shared` is a Rhai RESERVED keyword, so `kv::shared(...)` is a parse
  error. Renamed the handle constructor to `kv::shared_collection(...)`
  (keeps the user's "shared" intent; unambiguous). Updated everywhere.
- CLI manifest: `collections = [...]` on `[group]` only (ManifestApp has no such
  field + deny_unknown_fields → an app manifest carrying it is a hard error);
  Manifest::collections() accessor; build_bundle emits it.
- plan/apply: a `collection` row group in `pic plan`; created/deleted counts in
  the apply summary; collections threaded through PlanDto/NodePlanDto/
  ApplyReportDto.
- read-only `pic collections ls --group` → GET /admin/groups/{id}/collections
  (viewer+), backed by ApplyService::collection_report + CollectionInfo.
- journey: a group declares `catalog`; app A writes, app B (same subtree) reads
  it back; a sibling-subtree app gets CollectionNotShared; `collections ls` +
  re-apply NoOp. Full suite 114/114.
- docs: groups-and-project-tool §11.6 (KV-only MVP shipped + deferrals),
  sdk-shape.md (the shared-collection handle + trust model), CLAUDE.md.

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

crates/picloud-cli/src/manifest.rs

@@ -111,6 +111,17 @@ impl Manifest {
         }
     }
 
+    /// This node's declared shared group-collection names (§11.6). Authored on
+    /// `[group]` nodes only — an `[app]` manifest carrying `collections` is a
+    /// hard parse error (`ManifestApp` has no such field + `deny_unknown_fields`).
+    #[must_use]
+    pub fn collections(&self) -> &[String] {
+        match &self.group {
+            Some(g) => &g.collections,
+            None => &[],
+        }
+    }
+
     /// Load and parse the manifest at `path`.
     pub fn load(path: &Path) -> Result<Self> {
         let body =
@@ -238,6 +249,13 @@ pub struct ManifestGroup {
     /// See [`ManifestApp::extension_points`]. A key of the `[group]` table.
     #[serde(default, skip_serializing_if = "Vec::is_empty")]
     pub extension_points: Vec<String>,
+    /// `collections = ["catalog", …]` (§11.6) — shared KV collection names this
+    /// group offers as cross-app-shared (read by any app in the subtree,
+    /// written by an authenticated editor+). Group-only: there is no
+    /// `collections` key on `[app]`. The data lives in `group_kv_entries`;
+    /// pruning a name removes the declaration, not the data.
+    #[serde(default, skip_serializing_if = "Vec::is_empty")]
+    pub collections: Vec<String>,
 }
 
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]