PHP use-import map 4/5: positive alias binding via namespace index

[filipechagas]

Parent

Spec: #18 (ticket 4/5). Additive recall win; not needed to close #16.

What to build

Use the use-import map to positively bind a short receiver-type name when several same-short-named classes exist in the corpus: use App\Services\X; should select App\Services\X among the candidates (today the len != 1 guard at extract.py:3247-3260 refuses).

Requires a (namespace, simple_name) -> node_id index for PHP, sourced from the php_class_fqns per-file payload (engine.py:5285-5290), consulted by PhpNameResolver (#21).

Constraints

• Additive-only: may add or re-point edges, never delete. Opposite risk profile to PHP use-import map 3/5: PhpNameResolver decisive refusal (closes #16) #21 — keep the diffs separate.
• Multi-namespace files: follow the per-declaration policy (_php_pre_scan_class_namespaces, engine.py:183-237), not resolution.py:2541-2542's bail — spec Spec: PHP use-import-map awareness for member-call resolution (upgrade path for #16) #18 decision.
• Must ship in the same release as PHP use-import map 5/5: incremental-rebuild parity marker for declared FQNs #23. Without the carry-over marker, incremental rebuilds silently lose every edge this ticket adds when the defining file is unchanged.
• Decoy discipline: each positive test carries same-short-named decoys in other namespaces asserted to get NO edge.

Acceptance criteria

• Two in-corpus App\A\X / App\B\X; caller with use App\A\X; and typed receiver binds to App\A\X only
• Aliased import use App\A\X as Y; with private Y $r; binds to App\A\X
• No use statement → today's unique-short-name behavior unchanged
• Full suite green vs current v8 baseline; CHANGELOG line for the added-edge class

Blocked by

#21. Releases only together with #23.