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/collide/collide-circles.md

@@ -1,22 +0,0 @@
----
-id: collide-circles
-name: Collide.circles
-category: collide
-kind: namespace-method
-tokens: Collide.circles
-sig: Collide.circles(ax, ay, ar, bx, by, br) -> bool
-tip: Do two circles overlap?
-order: 2
-ns: Collide
-member: circles
----
-
-Returns <code>true</code> when circles centred at <code>(ax, ay)</code> and <code>(bx, by)</code> with radii <code>ar</code> and <code>br</code> overlap — that is, when the distance between centres is at most <code>ar + br</code>. It compares squared distances internally, so there is no square root and no precision loss.
-
-```ludic
-program Demo {
-  handler Step phase Update {
-    if Collide.circles(px, py, 8, ex, ey, 8) { collide() }
-  }
-}
-```