feat(support): bring Collection/Arr to L13 shape (task 3.3b)

[agissept]

Stacked on #37 (task 3.3a). Completes Wave 1 — the fork's Collection surface now matches Laravel 13, so the app can start exercising L13 Collection idioms.

What

Copy the v13 collection-family into the fork's Support tree, sourced verbatim from the clean v13.30.1 tag (git show) — not the local ../framework working tree (it sits on an inconsistent merge branch).

New: Enumerable, Traits/EnumeratesValues, LazyCollection, HigherOrderCollectionProxy, Item/MultipleItemsFoundException, functions.php (enum_value), Contracts/Support/CanBeEscapedWhenCastToString, and a minimal SortDirection enum (v13 references it from Collection::sort*() but ships no defining file — dangling even upstream; only ::Ascending/::Descending are ever used).

Deliberate deviations from verbatim copy

• Strip TransformsToResourceCollection — it pulls in Http\Resources and would undo the SCC-1 decoupling from refactor(support): break SCC-1 — decouple Support from Http & Container (task 3.3a) #37.
• Keep the 4.2 holdovers the fork's Database layer still calls (Collection::lists()/fetch(), Arr::build()/fetch()); removed later in task 2.5.

Reconciliation

• Arr (kept, not replaced — first/last already v13 value-first): add from/mapWithKeys/partition/select; flip Arr::where to v13 value-first (ARRAY_FILTER_USE_BOTH) and fix its whereNotNull + UrlGenerator callers.
• Eloquent\Collection (only subclass): widen contains()/unique() and delegate the v13 args to parent::; drop the redundant max()/min() overrides (base v13 handles model collections via data_get).
• Tests updated to v13 semantics (immutable sort, key-preserving chunk/takeLast, keys()→Collection, random-on-empty throws, toJson via jsonSerialize, offsetExists via isset).
• MorphTo::gatherKeysByType gets ->values() for v13 map key-preservation.

⚠️ For app integration

v13 Collection::map preserves keys where 4.2 reindexed. Only one fork site surfaced (MorphTo, fixed). App code that assumes map() reindexes may silently produce keyed arrays — worth watching when you wire this fork into the app. Broader app sweep is a separate deferred task.

Verification

• Full fork suite green: 1641 passed, 0 failures.
• SCC-1 stays broken (grep Support→Http/Container concrete = 0).
• Convergence ratchet tightened: macroable_trait 14→12, legacy_contracts 50→37.

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