feat(wam-clojure): add lowered emitter scaffold

[s243a]

Summary

Add the first implementation slice of the Clojure lowered-WAM tier:

• new wam_clojure_lowered_emitter.pl
• focused unit tests for parsing, lowerability, naming, and first-slice
  emission

This is the first implementation PR that follows the merged lowered-tier
design docs. It does not wire the new tier into
wam_clojure_target.pl yet.

What’s included

New module

• src/unifyweaver/targets/wam_clojure_lowered_emitter.pl

It provides:

• wam_clojure_lowerable/3
• is_deterministic_pred_clojure/1
• clojure_lowered_func_name/2
• lower_predicate_to_clojure/4

New tests

• tests/test_wam_clojure_lowered_emitter.pl

Coverage includes:

• deterministic predicate lowerability
• conservative clause-1 lowerability for multi-clause predicates
• rejection of unsupported shapes such as switch_on_constant
• lowered function-name normalization
• first-slice emitted Clojure function shape
• call_foreign presence in the lowered scaffold

Scope

This PR is intentionally narrow.

It adds the missing lowered-emitter module but does not yet:

• route hybrid Clojure predicates through the new tier
• change wam_clojure_target.pl
• add atom/functor interning
• change LMDB/runtime behavior

That keeps the first implementation step small and testable.

Why this is next

The main architectural gap versus Rust was the lack of a real hybrid
middle tier between:

• classic native clause lowering
• and full WAM interpretation

This scaffold establishes that missing tier without prematurely
entangling it with routing, runtime changes, or interning work.

Follow-up

The next PR should:

1. wire the lowered tier into wam_clojure_target.pl
2. add target-level routing for:
   • native
   • lowered WAM
   • foreign/kernel
   • full WAM fallback
3. then begin atom/functor intern-table scaffolding