feat: anonymous record literal shorthand {field:val} without typedef

[danieljohnmorris]

Summary

• Adds {field:val field2:val2} syntax for ad-hoc structural records without a prior type declaration
• Type checker synthesises a structural Ty::AnonRecord that unifies with any record of the same field shape
• Runtime delegates to the existing Value::Record path — zero overhead vs named records

What's included

• Parser: is_anon_record_literal lookahead ({ ident : ...) unambiguously distinguishes from brace-blocks and destructure patterns; wired into can_start_atom and parse_atom
• AST: Expr::AnonRecord { fields } with full coverage in alias resolution, desugar, field-collection, free-var collection, and all codegen passes
• Type checker (verify.rs): Ty::AnonRecord(Vec<(String, Ty)>) — field access, destructure binding, with update, and structural unification (order-independent field matching)
• Interpreter: eval_expr arm emits Value::Record { type_name: "__anon", fields }
• VM (RegCompiler): synthesises a shape-stable type name __anon_<sorted_fields> so two literals with the same field set share a registry entry; uses existing OP_RECNEW / OP_RECNEW_EMPTY paths
• Codegen: fmt.rs and python.rs handle the new variant
• Example + tests: examples/anon-record.ilo — 9 test cases covering construction, field access, pass-to-fn, return-from-fn, destructure, and with update (all pass)

Test plan

• cargo build — clean
• ilo test examples/anon-record.ilo — 9/9 pass
• cargo test — all tests pass (pre-existing body_is_thin_bootstrap failure is unrelated to this PR and already present on main)

Follow-ups

• Type-directed coercion: allow passing {name:t} where a named record with a name field is expected (structural subtyping)
• with adding new fields to anonymous records is currently permitted by the type checker; may want to restrict or document
• Python codegen emits a plain dict; could add _type sentinel if needed for downstream tooling

Closes ILO-54

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 81.36882% with 49 lines in your changes missing coverage. Please review.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/verify.rs	75.86%	14 Missing ⚠️
src/vm/mod.rs	82.14%	10 Missing ⚠️
src/codegen/fmt.rs	0.00%	6 Missing ⚠️
src/codegen/python.rs	40.00%	6 Missing ⚠️
src/parser/mod.rs	82.35%	6 Missing ⚠️
src/graph.rs	0.00%	4 Missing ⚠️
src/interpreter/mod.rs	72.72%	3 Missing ⚠️

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