Supertype patterns silently never match — reject them until implemented

[zharinov]

Problem

Tree-sitter grammars define supertypes — abstract categories like statement in JavaScript that group concrete node kinds (lexical_declaration, expression_statement, …). Tree-sitter never produces a node whose kind is the supertype itself, so a pattern like (statement) can never match anything. Plotnik currently accepts such patterns and emits bytecode that silently never matches:

cargo run -p plotnik -- run -q 'Q = (program (statement)* @s)' -s 'let x;' -l javascript
# → {"s":[]}, exit 0   (silently empty — the worst failure mode)

The narrowing syntax — native (statement#lexical_declaration) and the deprecated tree-sitter (statement/lexical_declaration) — parses and type-checks, but the subtype is recorded in the CST and then dropped: the pattern collapses to the bare supertype and silently never matches either. (The syntax has landed; semantics are deliberately deferred to this issue and #423.)

Approach (interim — fail loudly)

This issue is NOT about implementing supertypes (see #423). The goal is to convert the silent no-match into an error so the feature can be safely postponed:

• At analyze/link time, when a named node's kind resolves to a supertype of the linked grammar, emit a diagnostic: the supertype name, a note that supertype patterns are not yet supported, and a suggestion to list concrete kinds in an alternation instead. When a subtype refinement is present in the CST, name it in the message.
• This fires for all three spellings: (statement), native (statement#lexical_declaration), and deprecated (statement/lexical_declaration) — they share one AST (subtype ignored). The / form additionally still emits its parser deprecation warning; the link-time rejection stacks on top.
• The grammar side already has the data: Grammar::subtypes() exists in plotnik-core (currently zero consumers).
• Diagnostics live in crates/plotnik-compiler/src/diagnostics/; resolution happens in crates/plotnik-compiler/src/analyze/link.rs.

Acceptance

• check fails with the diagnostic for (statement), (statement#...), and (statement/...) on linked queries.
• The run repro above becomes a compile-time error instead of {"s":[]}.
• Unlinked compilation (no -l) is unaffected — supertypes are a grammar concept; without a grammar there is nothing to resolve against. The parser-level /→# deprecation warning still applies unlinked.