batch: no func_start rule -- zero units extracted from scripts built on call :label subroutines #3338

Problem

batch has no func_start rule (languages/batch.py never defines the key), so the engine extracts zero units from batch scripts, even ones built around call :label subroutines. Measured on language-crucible v1.4.0:

batch is also missing from docs/func_start_rule_contract.md's audit table, so this is an unaudited gap, not a stated absence.

Consequences

• Every per-unit signal is empty for batch: function counts, complexity, unreferenced_by_name, and calls_out_to.
• unreferenced_by_name: audit the other case-insensitive languages for the #3198 identifier lexicon #3225 had to leave batch out of identifier_case because there is no unit to measure. Batch labels are case-insensitive, so it belongs in the cobol usage_status: entry paragraph flagged, case-sensitive matching, and NAME-EXIT counts as a reference to NAME #3198 lexicon once units exist.
• The Epic: detect project-local idiom wrappers as a fact channel (follow-up to #3003) #3313 wrapper channel sees no batch helpers.

Scope question to settle first

A batch :label is both a goto target and a call :label subroutine, and the language doesn't distinguish them syntactically. Decide against the corpus whether func_start means:

• every :label, or
• only labels that are the target of a call : somewhere in the file, which is the only invoke-by-name form.

Then run the harden-language-extraction / rule-contract-audit process and add a batch row to the func_start contract.

Found during epic #3313 / #3225.