Add Polonius-like location-sensitive loan analysis

[itsfuad]

Track loans through CFG locations and origin relationships so borrow validity is not limited to lexical approximation.

Scope:

• Make loan liveness location-sensitive.
• Track origin relationships through CFG facts.
• Preserve existing ownership, move, cleanup, and match-temporary boundaries.
• Use Rust Polonius concepts as design input without copying Rust surface semantics.

Non-scope:

• Do not use this issue for enum match ownership/drop convergence.
• Do not fold storage ownership, moves, or cleanup planning into loan analysis.
• Do not remove the need for explicit per-path cleanup evidence.

Related:

• Allow dead enum match carriers after mixed arm moves #101 tracks match ownership/drop-state convergence for dead carriers after mixed arm moves.