refactor(stdlib): de-abbreviate namespaces (Mem/Sys/Net/Collide)

Expand the abbreviated public namespaces to full words, part of the
language-wide de-abbreviation pass:
  Mem -> Memory, Sys -> System, Net -> Network, Collide -> Collision

Math stays (universally accepted, like int/bool). Renames the dispatch
strings, LSP signatures, docs (dirs, files, frontmatter), and the
inventory manifest; behavior is byte-identical (the bare rt_ targets are
unchanged). Reseeded; C-free bootstrap fixpoint holds; all suites green.

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

docs/language/system/system-stdout.md

@@ -0,0 +1,14 @@
+---
+id: system-stdout
+name: System.stdout
+category: system
+kind: namespace-method
+tokens: System.stdout
+sig: System.stdout() -> ptr
+tip: The standard output handle.
+order: 12
+ns: System
+member: stdout
+---
+
+Returns the standard-output file handle, for <code>System.file_write</code>.