[FEATURE] Residue of the layout and GitTarget API-wave work

[sunib]

The single issue that replaces #294 and #296, both closed as shipped. Everything larger has landed:
spec.suspend, status.placement, the ambiguous-root refusal and the reconcile-request annotation
(#326), useKustomize and serializeNamespace (#328), the commitWindow / commit.message move and
the source-scope deletion (#330), the reference collapse onto meta.LocalObjectReference, the
ClusterWatchRule.spec.rules[].scope removal and the by_type / default metric split (#333).

What is left is small and additive. None of it needs a breaking release.

Legibility (from #296)

• Express the canonical path as a template constant rendered through RenderPlacementTemplate,
  pinned byte-for-byte against ResourceIdentifier.ToGitPath() across cluster-scoped, core,
  grouped and sensitive identities. Retires the hand-written canonicalPath in
  internal/manifestanalyzer/placement.go.
• {kindLower} as a placement template variable, plus the single-namespace recipe and its
  identity caveat in docs/configuration.md.
• One name for the built-in path across docs/architecture.md, docs/configuration.md and the
  CRD comments: "canonical", since placement.default is a user declaration.

Riders (from #294)

• CommitRequest.spec.author, SAR-guarded (consumer ask ci(deps): Bump softprops/action-gh-release from 1 to 2 #5).
• The CommitRequest lifecycle hole: a TTL or an ownerRef, and the delete verb (F10).
• The default ClusterProvider not-found message (B6).

Decided, and dropped

• No corev1.Event on the GitTarget for a fall-back to canonical. The metric names the target and
  the missing byType key, and status.placement is the durable record. Two surfaces are enough.
• No TooManyStreams cap. It was queued to bound the per-namespace fan-out of sourceNamespace: "*",
  which feat(api)!: move commit batching onto GitTarget, delete allowedSourceNamespaces, and make sourceNamespace "*" cluster-wide #330 deleted outright. It was never in code; the docs no longer promise it.
• No movable destination (consumer ask deps(deps): Bump github.com/onsi/gomega from 1.36.1 to 1.38.0 #6, status.observedDestination). gitProviderRef, branch
  and path stay immutable; a folder moves by delete-and-recreate.