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/collision/collision-circles.md

@@ -0,0 +1,22 @@
+---
+id: collision-circles
+name: Collision.circles
+category: collision
+kind: namespace-method
+tokens: Collision.circles
+sig: Collision.circles(ax, ay, ar, bx, by, br) -> bool
+tip: Do two circles overlap?
+order: 2
+ns: Collision
+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 Collision.circles(px, py, 8, ex, ey, 8) { collide() }
+  }
+}
+```