Dimensionality check misses captures inside enum branches

[zharinov]

A quantifier with captures inside it needs a struct/row capture. check enforces this for sequences but not for enum (labeled alternation) branches.

Repro

# enum branch with an internal capture, no row capture — accepted (wrong):
cargo run -p plotnik -- check -l javascript -q 'Q = [A: (identifier) @id]*'
# []   (no error)

# same shape written as a sequence — correctly rejected:
cargo run -p plotnik -- check -l javascript -q 'Q = {(identifier) @id}*'
# error: quantifier `*` contains captures (`@id`) but has no struct capture

Expected

[A: (identifier) @id]* should raise the same strict_dimensionality_violation error, since @id is a capture inside the quantified body.