feat(apply): declarative extension_points reconcile (§5.5 C3)

Thread extension-point markers through the manifest and the apply engine —
a name-only resource modeled on `secrets` (shape) with `vars`-style
create/prune write behavior.

- manifest: top-level `extension_points = ["theme", …]` (allowed on app and
  group; overlay stays base-only via deny_unknown_fields); `build_bundle`
  emits the names.
- apply_service: `Bundle.extension_points`, `CurrentState.extension_point_names`,
  `Plan.extension_points` (+ is_noop), `diff_extension_points`
  (declared→Create / live-undeclared→Delete / else NoOp), `load_current`
  loads them, `reconcile_node_tx` inserts on Create + deletes on prune,
  `state_token_with_names` folds in `ep|<name>`, `validate_bundle` rejects
  duplicates + reserved names, `ApplyReport` gains created/deleted counts.
- CLI client + plan/apply rendering: `extension_points` in PlanDto/NodePlanDto/
  ApplyReportDto, an `extension_point` row group in `pic plan`, a count in the
  apply summary.

pull sets it empty for now (wired to the read endpoint in C4).

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

crates/picloud-cli/src/cmds/apply.rs

@@ -84,6 +84,13 @@ pub async fn run(
                 "+{} ~{} -{}",
                 report.vars_created, report.vars_updated, report.vars_deleted
             ),
+        )
+        .field(
+            "extension_points",
+            format!(
+                "+{} -{}",
+                report.extension_points_created, report.extension_points_deleted
+            ),
         );
     for w in &report.warnings {
         block.field("warning", w.clone());
@@ -151,6 +158,13 @@ pub async fn run_tree(
                 "+{} ~{} -{}",
                 report.vars_created, report.vars_updated, report.vars_deleted
             ),
+        )
+        .field(
+            "extension_points",
+            format!(
+                "+{} -{}",
+                report.extension_points_created, report.extension_points_deleted
+            ),
         );
     for w in &report.warnings {
         block.field("warning", w.clone());