[codex] Harden pubpunk target-instance contract guards

[t3chn]

Summary

• harden pubpunk drafter prompt normalization so target-instance bounded slices do not inherit init/bootstrap scaffold semantics from Do not modify ... init behavior
• align adapter context-pack and required-symbol extraction so do not modify is treated the same as other negative clauses during target ranking and explicit symbol checks
• add exact regressions for pubpunk target-instance draft normalization and target-loader symbol anchoring

Why

Target-instance contracts were being misclassified or semantically defocused because negation parsing was inconsistent across drafter, context-pack, and execution symbol guards.

Impact

• core-only target-instance contracts stay bounded to crates/pubpunk-core/src/lib.rs
• init/bootstrap scaffold noise is pruned from drafted contracts
• target-loader slices keep focusing on TargetInstanceConfig and load_target_instances instead of forbidden symbols like validate_report

Issue ID: N/A

Test Plan

• cargo test -p punk-adapters
• cargo test -p punk-orch pubpunk_