demos: add cloud-burst example manifests

[nerdalert]

What

Adds reference manifests under demos/grid-cloud-burst/example-manifests/ so the cloud-burst demo's policy concepts are concrete and applyable, not just described in prose.

File	Demonstrates
01-local-sim-pools.yaml	Deterministic local providers with a controlled queue metric (reproducible admission/burst without real load)
02-gridnetwork.yaml	Composed burst policies — scoringPolicy / admissionPolicy (stabilized enter 0.85 / exit 0.70) / selectionPolicy + placementPolicy / routingPolicy. Bursting emerges from composition; there is no dedicated switch
03-grid-sites-and-providers.yaml	Local pool (backendKind: local) + OpenAI overflow (backendKind: api_provider, auth.manual: true) — distinct backend class keeps overflow in its own fallback group
04-bedrock-overflow.yaml	A second, genuinely distinct overflow cloud (generic HTTP hop) — burst amount is independent from burst destination
05-consumer-praxis-soft-quota.yaml	Consumer gateway: token_rate_limit with enforcement: soft (over-budget → served + flagged, never 429) alongside intelligent_route
06-provider-praxis.yaml	Provider gateway: peer_identity_trust (fail-closed) → provider_route → credential_inject
README.md	Apply order, prerequisites, placeholder notes, and a mapping from each file to the demo's user stories

Notes

• Files are copied from the working demo; a directory README.md documents apply order and how each file maps to a user story.
• Placeholder-bearing files (site IDs, gateway IPs, trust fingerprints, and Praxis config template vars) are rendered per-cluster by the demo's tooling. No credentials are included — the OpenAI overflow references a openai-api-key secret via auth.manual: true.
• Purely additive: a new subdirectory under the existing demos/grid-cloud-burst/.

[github-actions]

Non-conforming commit subjects (expected type(scope): summary, ≤72 chars, types: build/chore/ci/docs/feat/fix/perf/refactor/test):

• bde399c: demos: add cloud-burst example manifests

Amend with git commit --amend or rewrite with git rebase -i.