feat(project-tool): per-env approval-policy gating (§4.2/§6)

Salvaged from the superseded feat/hierarchies-extension-points branch (M5),
re-ported onto main's evolved tree-apply engine. Fills the §7/§11.1 "per-env
approval-policy gating" that main's design doc still lists as intended but
unbuilt.

A project's root manifest declares which environments require explicit
approval; `pic apply --dir --env <e>` to a confirm-required env needs an
explicit `--approve <e>` (a blanket `--yes` does NOT cover it). The approval
is admin-gated (admin on every declared node) and audited, and the policy
folds into the bound-plan token.

- manifest: `[project]` block → ManifestProject { environments[{name,confirm}] },
  root-manifest-only (rejected elsewhere by build_tree).
- discover: build_tree emits `project` into the bundle from the root manifest.
- apply_service: TreeBundle.project + ProjectPolicy; policy folds into the
  state_token; plan surfaces approvals_required; ApplyError::ApprovalRequired
  → 409.
- apply_api: enforce_env_approval (after authz_tree) — refuses a gated env not
  in approved_envs, requires AppAdmin/GroupAdmin on every declared node on
  approval, audits. Server re-derives policy from the bundle (authoritative).
- CLI: --approve (repeatable); resolve_approvals refuses a gated env
  non-interactively, prompts on a TTY; plan renders gated envs. Single-node
  apply --file refuses a confirm-required env and directs to --dir.
- approval journey + manifest/ProjectPolicy unit tests. No migration (policy
  lives in the manifest, like takeover/blast-radius).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

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

@@ -116,6 +116,7 @@ fn scaffold_manifest(slug: &str, name: &str) -> Manifest {
             extension_points: Vec::new(),
         }),
         group: None,
+        project: None,
         scripts: vec![ManifestScript {
             name: "hello".into(),
             file: "scripts/hello.rhai".into(),