feat(lang): #76 namespace block form with export/internal visibility

`namespace Name { export function foo(...) ... internal function bar(...) ... }`
declares a Name.* namespace once and controls its public surface declaratively,
instead of annotating every function with @Namespace(Name). Inside the block
each `function short(...)` is emitted as `namelower_short`; export (the default)
makes it callable as Name.short(...), internal keeps it a private helper
(emitted, callable by short name from siblings — calls are rewritten — but
Name.internalOne() is a compile error). Block sugar for the per-function
@Namespace annotation; a package's public API reads at a glance. Namespaces
declared the old way are unchanged (gameplay_foundation still passes).

namespace added to LUDIC_KW_DECL + JetBrains/TextMate + docs page + inventory
(vocab/impl/docs checks green). Example namespace_block (export + internal +
sibling calls + internal-visibility compile error verified). Full suite 116/0,
fixpoint holds.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/language/structure/kw-namespace.md

@@ -0,0 +1,28 @@
+---
+id: kw-namespace
+name: namespace
+category: structure
+kind: keyword
+tokens: namespace
+sig: namespace Name { export function foo(…) … internal function bar(…) … }
+tip: Group functions into a Name.* namespace and control its public surface.
+order: 16
+---
+
+A <code>namespace</code> block declares a <code>Name.*</code> namespace once and controls its public surface declaratively, instead of annotating every function with <code>@Namespace(Name)</code> one at a time. Inside the block each <code>function short(…)</code> is emitted as <code>namelower_short</code>; an <code>export</code> function (the default) is callable from anywhere as <code>Name.short(…)</code>, while an <code>internal</code> function is a private helper — emitted, and callable by its short name from other functions in the same block, but not part of the <code>Name.*</code> surface (calling <code>Name.internalOne()</code> is a compile error). It is the block sugar for the per-function <code>@Namespace</code> annotation, so a package's public API reads at a glance.
+
+Sibling calls inside the block use the short name (<code>base()</code>), and the compiler rewrites them to the emitted name — so a namespace reads like a self-contained module.
+
+```ludic
+program Demo {
+  namespace Combat {
+    export function amount() -> int { return base() + 5 }
+    internal function base() -> int { return 10 }
+    export function double(n: int) -> int { return n + n }
+  }
+  entry {
+    print(Combat.amount())      # 15
+    print(Combat.double(21))    # 42
+  }
+}
+```