feat(project-tool): bound-plan staleness check (content fingerprint)

`pic plan` now records a fingerprint of the live state it diffed against;
`pic apply` replays it and the server refuses (HTTP 409) if the app
changed underneath the reviewed plan — the §4.2 "apply exactly what you
reviewed" guarantee, in its content-addressed form (no migration, no
changes to interactive write paths).

Server (manager-core):
- `state_token(CurrentState)`: deterministic FNV-1a fingerprint over what
  the diff keys on — script name+version (version bumps on any edit),
  route identity+binding/attrs, trigger membership+enabled, secret names.
  Order-independent; a collision can only yield a false "unchanged", never
  a false refusal.
- `plan` returns it (flattened onto the plan JSON, so the wire stays
  additive); `apply` takes an optional `expected_token` and, under the
  apply lock before any write, returns `StateMoved` (409) on mismatch.

CLI:
- `.picloud/` link state (`linkstate`): `pic plan` writes the token scoped
  to the app slug; `pic apply` replays it, then clears it on success (the
  token is single-use — the next apply re-plans). `--force` skips the
  check; apply with no recorded plan still works standalone (today's
  behavior). `.picloud/` is already gitignored by `pic init`.

The tree-structure version (the other half of §4.2's counter) stays a
deliberate no-op until groups exist — it only guards reparent/structural
moves, which don't exist single-app.

Tested: state_token unit test (stable/order-independent/sensitive) + a
staleness journey (plan → out-of-band deploy → apply refuses → --force
applies); manager-core lib 363 + cli bins 31 + 13 journeys green; clippy
-D warnings clean.

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

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

@@ -23,6 +23,16 @@ pub async fn run(manifest_path: &Path, mode: OutputMode) -> Result<()> {
     let bundle = build_bundle(&manifest, base_dir)?;
 
     let plan = client.plan(&manifest.app.slug, &bundle).await?;
+    // Record the bound-plan token so a subsequent `pic apply` can detect the
+    // app changing underneath the reviewed plan (best-effort — a read-only
+    // plan still succeeds if the project dir isn't writable).
+    if !plan.state_token.is_empty() {
+        if let Err(e) =
+            crate::linkstate::write_plan(base_dir, &manifest.app.slug, &plan.state_token)
+        {
+            eprintln!("warning: could not record plan state for `pic apply`: {e}");
+        }
+    }
     render(&plan, mode);
     Ok(())
 }