Add semantic const evaluation

[itsfuad]

Summary

• add semantic const-eval query support after resolution and before typechecking
• keep arithmetic folding in shared constvalue, including cached const identifiers retyped under expected/common numeric context
• move AST type syntax text onto TypeExpr.TypeText() methods and remove parser/IR formatting ownership leaks
• move MIR static data generation to semantic const values and emit LLVM-valid float static literals
• move fixed-array const-index diagnostics into typechecker and materialize const indexes during HIR lowering
• keep HIR folding optimization-only for array bounds; backend array bounds remain fallback/invariant checks
• add ship one-word agent workflow trigger for commit/PR/merge/project automation

Validation

• env GOCACHE=/tmp/peeper-go-cache go test ./internal/frontend/ast ./internal/frontend/parser ./internal/semantics/consteval ./internal/ir/mir ./internal/pipeline -count=1 -timeout 120s -p 1
• env GOCACHE=/tmp/peeper-go-cache go test ./... -count=1 -timeout 120s -p 1
• env GOCACHE=/tmp/peeper-go-cache go run ./scripts/bundle.go
• ./build/bin/peeper check x_test/review_consteval_gaps/src/main.peep
• ./build/bin/peeper check x_test/runtime_numbers/src/main.peep
• git diff --check

Follow-up

• Updates Implement array and slice value semantics #27.
• Dynamic fixed-array indexes are explicitly rejected until runtime bounds policy is designed.
• Imported/qualified const contexts, array-length const contexts, and const fn evaluation remain future consteval work.