chore: version 1.51.0, path-dep the wasm examples, README notes

- socktop, socktop_agent, socktop_connector -> 1.51.0.
- socktop_wasm_test and zellij_socktop_plugin consume the in-repo
  connector via path deps so wasm-feature API drift is caught at PR time
  instead of after publish. Immediately proved out: the wasm requests
  module needed the new sampled_at_ms field, invisible to native builds.
- zellij plugin gains the standalone [workspace] marker (it could not be
  cargo-checked in-tree at all before). NOTE: its lib.rs has pre-existing
  compile errors unrelated to the connector (static mut STATE conflicts
  with register_plugin!, missing BTreeMap import) — needs its own rework,
  out of scope here.
- README: sampled_at_ms in the example payload.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

socktop_wasm_test/Cargo.lock

@@ -475,9 +475,7 @@ dependencies = [
 
 [[package]]
 name = "socktop_connector"
-version = "0.1.5"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "3a63dadaa5105df11b0684759a829012257d48e72a469cc554c0cf4394605f5a"
+version = "1.51.0"
 dependencies = [
  "flate2",
  "js-sys",