refactor(compiler): unify boundary quantifier lowering

[zharinov]

Boundary-aware quantifiers had two independent implementations of the same route topology: one for no-value flow and one for value-producing flow. Both computed reachable and productive boundary states, allocated loop labels, stitched repeat routes, and applied greediness. The copies could drift when boundary or navigation logic changed.

Quantifier lowering now owns that topology once. Each admitted iteration selects only its result handling:

Output mode	Iteration body
NoValue	Structural pattern lowering
Ordinary	Ordinary value lowering
CaptureType	Capture-type transformation

BoundaryOptionalOutput keeps a ? iteration's output mode together with the effects for its empty branch. No-value sequence lowering delegates to the shared kernel, so it no longer owns a quantifier loop or a separate boundary-port adapter.

A focused bytecode snapshot covers the previously unexercised no-value boundary routes for both ? and *. A two-entrypoint probe produced byte-for-byte identical artifacts before and after:

• bytecode dump: a523b89f1412ce84b92753efce1ddfd3c6d927a6e9812581350034bc4348b79f
• generated Rust: 8f74aa341891ed4eaca096c0941f65d9c7cf1a069e98dc964d8111c0dc8ff32f

Both entrypoints remain in one emitted artifact and can still be selected independently.