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/sys/sys-exit.md

@@ -1,14 +0,0 @@
----
-id: sys-exit
-name: Sys.exit
-category: sys
-kind: namespace-method
-tokens: Sys.exit
-sig: Sys.exit(code) -> void
-tip: End the process with a status code.
-order: 2
-ns: Sys
-member: exit
----
-
-Terminates the program immediately, returning <code>code</code> to the shell.