test(cli): extension-point journeys + node-key manifest fix + docs (§5.5 C5)

- Move the manifest `extension_points` from a top-level key to an `[app]`/
  `[group]` node key (`ManifestApp`/`ManifestGroup` + a `Manifest::extension_points()`
  accessor). A bare top-level array placed after the node header was silently
  re-nested by TOML into that table and dropped; as a node key it parses
  unambiguously wherever it sits. build_bundle/pull/init updated.
- Journeys (live server + Postgres): a group default body resolves for an
  inheriting app; the app provides its own module and OVERRIDES the EP (the
  inverse of the Phase 4b sealed import); `extension-points ls` shows the
  provider; a body-less EP with no provider fails `pic plan`.
- Re-bless the schema snapshot (new `extension_points` table).
- Docs: §5.5 marked complete (extension points ✅) + CLAUDE.md current-focus.

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

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

@@ -113,6 +113,7 @@ fn scaffold_manifest(slug: &str, name: &str) -> Manifest {
             slug: slug.to_string(),
             name: name.to_string(),
             description: None,
+            extension_points: Vec::new(),
         }),
         group: None,
         scripts: vec![ManifestScript {
@@ -139,7 +140,6 @@ fn scaffold_manifest(slug: &str, name: &str) -> Manifest {
         triggers: crate::manifest::ManifestTriggers::default(),
         secrets: crate::manifest::ManifestSecrets::default(),
         vars: std::collections::BTreeMap::new(),
-        extension_points: Vec::new(),
     }
 }