docs(readme): embedded quick-start run-through + trimmed Clients (#266)

* docs(readme): add embedded quick-start run-through + trim Clients

- Quick start: a copy-pasteable embedded (local file) run-through
  (schema → init → load → query → branch), followed by a "Storage backends"
  table that surfaces the one thing that changes across embedded / S3 object
  storage / RustFS-MinIO — the graph address — with a pointer to cluster mode
  for served multi-graph deployments.
- Clients: collapse to a two-line pointer (npm packages + omnigraph-ts repo);
  Python SDK marked coming soon.

* docs(readme,quickstart): fix init addressing + drop non-parsing schema commas

Addresses PR review (both verified against source):

- README "Storage backends": `init` takes the graph address as a positional
  argument, not `--store` (`Command::Init { uri: String }`) — Codex. Table now
  shows bare addresses and a note on which flag each verb uses.
- docs/user/quickstart.md: drop trailing commas in the schema. The .pg grammar
  (`prop_decl = { ident ~ ":" ~ type_ref ~ annotation* }`, node body
  `(prop_decl | body_constraint)*`, comma not in WHITESPACE) has no comma rule,
  so `name: String,` fails to parse — Greptile.

docs/user/quickstart.md

@@ -12,8 +12,8 @@ A schema (`.pg`) declares your node and edge types. Save this as `schema.pg`:
 
 ```
 node Person {
-  name: String,
-  title: String?,
+  name: String
+  title: String?
 }
 ```