docs: accuracy sweep + ship reified-T contract + reorganize playground

[math3usmartins]

Three threads landing together after the monorepo restructure merged:

1. Doc accuracy sweep against actual source.

   Cross-referenced each public README + docs/* against core/src/, tools/lsp/src/, and tools/phpstorm-plugin/src/. Findings + fixes:

   • tools/phpstorm-plugin/README.md: file-type table row was wrong (claimed com.intellij.fileType extension; reality is the plugin deliberately registers no <fileType> and uses a TextMate bundle via XphpBundleRegistrar -- see plugin.xml L93 rationale). Feature table expanded to mirror the full LSP surface enabled by LspCustomization (references, rename, documentSymbol, workspace/symbol). "Semantic tokens" dropped from the wired-up diagram (server doesn't advertise that capability).
   • tools/lsp/README.md: Layout block under-represented the code by ~50%. Added six missing handlers (TextDocument, References, Rename, DocumentSymbol, WorkspaceSymbol, FileWatcher) + FqnIndex
     • nine missing Resolver/ classes (CompletionIndex, CompositeClassLikeLookup, Workspace/FilesystemClassLikeLookup, GenericResolver, GenericParamRegistry, ReferenceFinder, RenameProvider, VarBinding, MethodCallSubstitution, etc.).
   • docs/generics.md: struck "bound checks on method-level type-params aren't enforced yet" -- they ARE, via GenericMethodCompiler -> Registry::checkBounds for both static-call and free-function paths (verified at L344, L402). Added matching note under "Free generic functions".
   • docs/roadmap.md: moved method-level bound validation Next ->
     Shipped > Function-level generics.
   • docs/generics-comparison.md: baseline para rewritten (dropped "post feat/generics-expansion" branch language); Tier 1 add T[] array-type sugar; verify ?T nullable specialization #4 "Already on the MVP-gaps list" replaced with current framing; Cross-language summary moved to the top as the first h2 (quick reference before the per-tier breakdown); bad example fixed -- Box/ with the false "Plastic extends Animal" claim replaced with Box/ (Dog actually extends Animal in playground/src/Models/).

2. Ship reified-T inside a generic body.

   The Specializer's substituting visitor at core/src/Transpiler/Monomorphize/Specializer.php:146 matches any bare single-segment Name node whose text equals a type-param key -- which is what every new T(...), T::class, T::method(...), instanceof T, T::$prop, and is_a($x, T::class) reduces to syntactically. So all of them are substituted uniformly at codegen, not as special cases. The machinery was fully general; what was missing was fixtures locking the contract so it can't silently regress.

   Added:

   • core/test/fixture/compile/reified_t/ (Reified template + Alpha
     • Beta models + Use site)
   • core/test/Transpiler/Monomorphize/ReifiedTypeParameterIntegrationTest.php (8 tests / 50 assertions: one per substitution form, plus a specialization-independence check, a runtime round-trip via exec(), and a php -l syntax-validity sweep)
   • playground/src/Containers/Reified.xphp + playground/src/Demos/ Reified.xphp (registered in playground/bin/run)

   Core test count: 184 / 495 -> 192 / 545. Docs updated to mark
   reified-T as Shipped (Tier 1 playground #5 retitled with a "shipped" tag,
   cross-language table row simplified, Next opportunities re-numbered;
   roadmap.md Shipped > Runtime semantics gets the new bullet).

3. Reorganize playground LSP fixtures.

   playground/bin/run had been failing on main because playground/src/Demos/GenericFunction.xphp and playground/src/Demos/Phase3TieBreak.xphp both declared function identity<T> in App\Demos. The Phase3* files are LSP-only fixtures (opened in PhpStorm to verify completion / hover / GTD), not executable demos, and don't belong in Demos/.

   Moved (git mv preserves history):

   • playground/src/Demos/Phase3{BoundAware,ClosedFile, ScopeAwareVars,StaticProp,TieBreak,Utf16}.xphp -> playground/src/LspFixtures/ (namespace App\Demos -> App\LspFixtures)
   • playground/src/Demos/Phase3SubclassProtected.xphp -> playground/src/Models/Wolf.xphp (the class is Wolf extends Animal in namespace App\Models; its prior location under Demos/ violated PSR-4)

   Two latent bugs surfaced once compile succeeded (both had been
   masked by the earlier duplicate-identity bail):

   • LspFixtures/Phase3BoundAware.xphp: type-arg new StringableBox<App\Models\Tag> was namespace-relative-resolved (i.e. App\<current-ns>\App\Models\Tag); changed to short form new StringableBox<Tag> matching the convention in Bounds.xphp.
   • Containers/InMemoryRepository.xphp::items(): new Collection<T>($this->items) was missing the spread operator; Collection(T ...$items) is variadic, so the array tripped a runtime TypeError. Fixed to new Collection<T>(...$this->items).

   playground/README.md tree refreshed to distinguish Demos/
   (executable, in bin/run's list) from LspFixtures/ (editor-only,
   compiled but not run).

Verification:
make -C core test/unit -> 192 tests / 545 assertions
make -C tools/lsp test -> 424 tests / 1244 assertions
playground/bin/run -> executes all 11 demos end-to-end,
including the new Reified demo