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/net/net-poll.md

@@ -1,14 +0,0 @@
----
-id: net-poll
-name: Net.poll
-category: net
-kind: namespace-method
-tokens: Net.poll
-sig: Net.poll(buf, cap) -> int
-tip: Read an inbound datagram.
-order: 1
-ns: Net
-member: poll
----
-
-Reads up to <code>cap</code> bytes of the next inbound datagram into <code>buf</code> and returns the byte count, or zero when none is waiting.