Labeled Block

Implement block:name { ... break:name value ... } labeled-block early exit per the approved proposal (compiler_repo/docs/ori_lang/proposals/approved/labeled-block-early-exit-proposal.md). The parser rejects block:r { } today (zero .ori corpus usage); grammar.ebnf:408 + the approved proposal define it, so the parser is incomplete. Block type = unified type of all break:label exit paths + final expr; bare break is loop-only (passes through); continue:block_label is an error; break/continue:loop_label are transparent through blocks.