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-rect_circle.md

@@ -0,0 +1,22 @@
+---
+id: collision-rect_circle
+name: Collision.rect_circle
+category: collision
+kind: namespace-method
+tokens: Collision.rect_circle
+sig: Collision.rect_circle(rx, ry, rw, rh, cx, cy, cr) -> bool
+tip: Does a rectangle overlap a circle?
+order: 3
+ns: Collision
+member: rect_circle
+---
+
+Returns <code>true</code> when the rectangle <code>(rx, ry, rw, rh)</code> overlaps the circle centred at <code>(cx, cy)</code> with radius <code>cr</code>. It finds the point on the rectangle nearest the circle's centre and checks whether it falls within the radius — the correct test for a round actor against a blocky tile.
+
+```ludic
+program Demo {
+  handler Step phase Update {
+    if Collision.rect_circle(tx, ty, 16, 16, bx, by, 6) { block() }
+  }
+}
+```