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>

examples/library/namespace_block.ludic

@@ -0,0 +1,20 @@
+# namespace_block.ludic — the `namespace Name { ... }` block form (#76). Declares
+# the namespace once and controls its public surface declaratively: `export`
+# functions are callable as Name.method, `internal` ones are private helpers.
+# Sibling calls inside the block use the short name.
+#
+# Deterministic; a full run prints:  15 42 100
+program NamespaceBlock {
+  namespace Combat {
+    export function amount() -> int { return base() + 5 }   # calls the internal sibling by short name
+    internal function base() -> int { return 10 }           # a private helper — not Combat.base
+    export function double(n: int) -> int { return n + n }
+    export function via_internal() -> int { return base() * 10 }
+  }
+
+  entry {
+    print(Combat.amount())          # 15 — 10 (internal base) + 5
+    print(Combat.double(21))        # 42
+    print(Combat.via_internal())    # 100 — reaches the internal helper from inside the namespace
+  }
+}