Track reference origins and borrow conflicts

[itsfuad]

Goal

Complete safe-reference lifetime enforcement without adding lifetime syntax.

Current Boundary

• &T and &mut T types, expressions, receivers, interface views, and reborrows are implemented.
• Reference-containing aggregate storage remains rejected.
• Reference returns remain rejected until origin summaries exist.
• Obvious same-expression alias conflicts and owner-move-while-borrowed checks are not implemented yet.

Scope

• Track origins for explicit borrows, receiver auto-borrows, field projections, reborrows, and borrowed interface values.
• Summarize which reference parameters may supply a returned reference.
• Allow safe parameter-origin reference returns while rejecting local-origin escapes.
• Reject conflicting shared/mutable borrows where overlap is known.
• Prevent moving or consuming an owner while derived references remain live.
• Keep conservative rejection for unresolved aggregate/index overlap.
• Keep v1 free of user-written lifetime parameters.

Validation

• Focused ownership/typechecker tests for return origins, reborrows, alias conflicts, and owner moves.
• Positive and negative x_test/ fixtures.
• HIR/MIR/backend smoke for accepted returned references.
• Full go test ./... and git diff --check.