docs: onboarding-first README + in-repo agent skill + drop RustFS script (#257)

* docs: optimize README for dev onboarding; fix 0.7.0 staleness

The README's setup half drifted from the shipped 0.7.0 CLI and led with the
heaviest path (Docker + RustFS). This reworks it for fast, correct onboarding:

README.md
- New zero-dependency "Your first graph in 60 seconds" hero: a fully
  copy-pasteable local file-backed loop (schema → init → load → query → branch).
- Add a correct "Serve it" section (cluster apply + omnigraph-server --cluster);
  the server is cluster-only on main, so the old positional-URI boot is gone.
- Demote the RustFS bootstrap to "rehearse the S3 path locally"; reframe the
  storage bullet as "filesystem or any S3-compatible store (AWS S3, R2, MinIO,
  RustFS)" — RustFS is a provider, not a storage class.
- Fix crate/MCP descriptions (query/mutate/load, not read/change/ingest).

docs/user/quickstart.md
- Fix the query example: `read --name <q> … <uri>` is removed — the query name
  is positional and the graph is addressed with `--store` (`omnigraph query
  find_people --query queries.gq --store graph.omni`).

scripts/local-rustfs-bootstrap.sh
- Convert to cluster mode: write a cluster.yaml (storage: s3://…), then
  validate → import → apply, load the fixture into the derived root with the
  now-required --mode, and serve with `omnigraph-server --cluster`. The old
  flow (`load` without --mode, `omnigraph-server <URI>` positional boot) no
  longer works on a cluster-only server.

* docs: move agent skill into the repo, add agent-setup snippet, drop rustfs script

skills/omnigraph
- The operational skill (formerly `omnigraph-best-practices` in the cookbooks
  repo) now lives with the engine it documents, co-versioned. Renamed to
  `omnigraph`; repository metadata repointed here.
- Broadened the description to trigger on intent — storing/retrieving/querying
  knowledge, agent memory, building a knowledge graph, operating Omnigraph — as
  well as on CLI/artifact sightings (stays ≤1024 chars).
- Install: `npx skills add ModernRelay/omnigraph@omnigraph`.

README
- New "Set it up with an AI agent" paste snippet: installs the skill, reads the
  docs (URL), browses the cookbooks, and asks the user about a use case before
  standing up a first graph.
- "Agent skill & starter graphs" section points at skills/omnigraph + cookbooks.

Drop scripts/local-rustfs-bootstrap.sh
- Not CI-tested (so it rotted: it broke on the cluster-only migration — positional
  server boot, load without --mode), demoed the now-optional S3 path, and was the
  most fragile artifact in the repo. Replaced with a "Testing against S3 locally"
  guide in deployment.md (docker run RustFS/MinIO + AWS_* env + cluster-on-S3).
  README/AGENTS references updated.

AGENTS.md

@@ -100,7 +100,7 @@ Full diagram and concurrency model: [docs/dev/architecture.md](docs/dev/architec
 | Audit / actor tracking | [docs/user/operations/audit.md](docs/user/operations/audit.md) |
 | Error taxonomy and result serialization | [docs/user/operations/errors.md](docs/user/operations/errors.md) |
 | Install (binary / Homebrew / source / channels) | [docs/user/install.md](docs/user/install.md) |
-| Deployment (binary / container / RustFS bootstrap / auth / build variants) | [docs/user/deployment.md](docs/user/deployment.md) |
+| Deployment (binary / container / S3-local testing / auth / build variants) | [docs/user/deployment.md](docs/user/deployment.md) |
 | CI / release workflows | [docs/dev/ci.md](docs/dev/ci.md) |
 | Code ownership (CODEOWNERS source of truth, roles, regeneration) | [docs/dev/codeowners.md](docs/dev/codeowners.md) |
 | Branch protection policy (declarative, applied via `scripts/apply-branch-protection.sh`) | [docs/dev/branch-protection.md](docs/dev/branch-protection.md) |
@@ -192,7 +192,7 @@ cargo test -p omnigraph-engine --features failpoints --test failpoints   # fault
 cargo build -p omnigraph-server --features aws   # AWS Secrets Manager bearer-token source
 ```
 
-S3-backed tests (`s3_storage`, and the S3 paths in server/CLI system tests) **skip** unless `OMNIGRAPH_S3_TEST_BUCKET` + `AWS_*` (incl. `AWS_ENDPOINT_URL_S3` for non-AWS) are set; CI runs them against containerized RustFS. `scripts/local-rustfs-bootstrap.sh` stands up a local S3 environment.
+S3-backed tests (`s3_storage`, and the S3 paths in server/CLI system tests) **skip** unless `OMNIGRAPH_S3_TEST_BUCKET` + `AWS_*` (incl. `AWS_ENDPOINT_URL_S3` for non-AWS) are set; CI runs them against containerized RustFS. To run RustFS/MinIO yourself, see [docs/user/deployment.md](docs/user/deployment.md) → *Testing against S3 locally*.
 
 CI does **not** run `clippy` or `rustfmt` as gates — but `cargo test --workspace --locked` is the exact gate, so run it before pushing. Two non-test CI checks: `scripts/check-agents-md.sh` (doc cross-link integrity — run it after moving/renaming docs) and OpenAPI drift (`crates/omnigraph-server/tests/openapi.rs` regenerates `openapi.json`; set `OMNIGRAPH_UPDATE_OPENAPI=1` to update the checked-in copy when a server/API change is intentional).
 
@@ -268,7 +268,8 @@ omnigraph policy explain --cluster ./company-brain --graph knowledge --actor act
 | HTTP server | — | Axum, OpenAPI via utoipa, bearer auth (SHA-256, AWS Secrets Manager option), `authorize_request` at the HTTP boundary (resolves bearer→actor, applies admission control), NDJSON streaming export, **cluster-only boot (RFC-011): always `--cluster <dir | s3://…>`, serving N graphs (N ≥ 1) under multi-graph routes + read-only `GET /graphs` enumeration + per-graph + server-level Cedar policies. Add/remove graphs via `cluster apply` and restart.** |
 | CLI with config | — | two-surface config (team `cluster.yaml` dir + per-operator `~/.omnigraph/config.yaml`), scope addressing (`--store`/`--server`/`--cluster`/`--profile`/defaults, RFC-011), aliases, multi-format output (json/jsonl/csv/kv/table) |
 | Audit / actor tracking | — | `_as` write APIs + actor map in commit graph |
-| Local RustFS bootstrap | — | `scripts/local-rustfs-bootstrap.sh` one-shot S3-backed dev environment |
+| Local S3 testing | — | run RustFS/MinIO + the `AWS_*` env; see [docs/user/deployment.md](docs/user/deployment.md) → *Testing against S3 locally* |
+| Agent skill | — | `skills/omnigraph` — operational playbook for driving Omnigraph; install with `npx skills add ModernRelay/omnigraph@omnigraph` |
 
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