Phase 6b: a handler's query is @Queries only; drop the signature clauses

The handler-signature `query (vars) [terms] where …` clause and the
`reads`/`writes` clauses overlapped the `@Queries` annotation (and each other):
two ways to attach a query to a handler. Consolidated on the decorator.

  - parse_system no longer parses `query`/`reads`/`writes` clauses; it keeps the
    postfix `@anno(...)` channel and `phase`. A handler's query is the prefix
    `@Queries(these: [...], on: Model)` annotation. Data-access hints are now
    `@Reads(...)`/`@Writes(...)` — absorbed by the generic annotation skipper,
    same parse-and-reserve status the old clauses had.
  - The inline `for (…) in query […] where …` statement is unchanged and still
    covers cross-property constraints / multiple kind filters. `query` stays a
    keyword there (now dispatched via is_id so the vocabulary check sees it).

examples/hello.ludic and examples/qdecl.ludic migrated to `@Queries` (qdecl now
demonstrates a per-property constraint + `on:` tag); outputs unchanged
(4 4 10 3 / 0 3 -2). LANGUAGE.md handler sections rewritten. Vocabulary: drop
`reads`/`writes` from CLAUSE (ludic_syntax.h, grammar, LudicTokens.kt).

Reseeded (21931 lines); C-free fixpoint holds; goldens identical; 17/17;
vocab + doc-fences clean.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

examples/hello.ludic

@@ -15,13 +15,12 @@ program Hello {
     }
   }
 
-  # a system can declare the entities it operates on: the body then runs once
-  # per match, with the components bound and self() giving that entity.
-  handler Move phase FixedUpdate
-    query (p, v) [Pos, Vel]
-  {
-    p.x = p.x + v.dx
-    p.y = p.y + v.dy
+  # a handler declares the entities it operates on with @Queries: the body then
+  # runs once per match, each property bound by name and self() giving that entity.
+  @Queries(these: [Pos, Vel])
+  handler Move phase FixedUpdate {
+    Pos.x = Pos.x + Vel.dx
+    Pos.y = Pos.y + Vel.dy
   }
 
   handler Report phase Update {