rename crates/ → vessels/ — El's word for buildable units

Per the consolidation onto El: 'crates' is the Rust word, 'vessel' is
El's (per spec/language.md §15). The directory rename is the structural
marker that this slot holds an El buildable unit, even if its current
contents are still Rust pending port.

Mechanical: git mv crates vessels, sed workspace members and any path
dependencies, update CI workflow paths, update README references.
Cross-repo path dependencies (`../foo/crates/bar`) updated workspace-
wide so cargo metadata still resolves where the Rust still builds.

ide/Cargo.toml

@@ -1,8 +1,8 @@
 [workspace]
 members = [
-    "crates/el-ide-server",
-    "crates/el-lsp",
-    "crates/el-plugin-host",
+    "vessels/el-ide-server",
+    "vessels/el-lsp",
+    "vessels/el-plugin-host",
 ]
 resolver = "2"
 
@@ -14,8 +14,8 @@ authors = ["Neuron Technologies"]
 
 [workspace.dependencies]
 # Internal crates (el-ide workspace)
-el-lsp         = { path = "crates/el-lsp" }
-el-plugin-host = { path = "crates/el-plugin-host" }
+el-lsp         = { path = "vessels/el-lsp" }
+el-plugin-host = { path = "vessels/el-plugin-host" }
 
 # Engram lang crates (path deps)
 el-lexer    = { path = "../el/engrams/el-lexer" }