lib/ww + wcc + w6c + wwdump: strip *arena cascade (γ-6)

amalloc has 0 callers post-γ-2; the *arena threaded through
newnode/newscope/newtype/prim/typesinit/type{ptr,slice,array,chan,
named}/lexinit/parserinit/joindotted/checkinit/arenau64tos/cgeninit
and the scope.a / tctx.a / lex.a / parser.a / checker.a / cgen.a
fields are vestigial.

Drop `import mem;` from 15 files, remove six struct fields, strip
*arena from 14 signatures, update ~120 call sites across lib/ww +
wcc + w6c + wwdump. selfhost/test/sym_link.ww fixture drops the
newarena/freearena probe; still exits 42 on scopedefine/scopelookup.
Both main.combined.ww auto-regenerated.

Comments retidied: typ.ww "once per arena" → "once per program";
parse.ww drops "arena-build" qualifier on joindotted; sym.ww drops
mem-sibling-imports rationale.

Verified 132/132 incl. 994_w6c_ww + 995_self_rebuild byte-identity
(the primary symmetric-stages gate).

selfhost/cmd/w6c/main.ww

@@ -14,7 +14,6 @@ package main;
 
 import os;
 import rt;
-import mem;
 import strings;
 import tok;
 import lex;
@@ -135,7 +134,6 @@ export fn main(argc: i32, argv: **u8) i32 = {
 		os.close(ofd);
 	};
 
-	let ar: *arena = newarena();
 	let nlen: u64 = cstrlen(src);
 	let view: str;
 	view.ptr = src;
@@ -143,10 +141,10 @@ export fn main(argc: i32, argv: **u8) i32 = {
 	let fname: str = strings.dup(view);
 
 	let l: lex;
-	lexinit(&l, ar, fname, buf, blen);
+	lexinit(&l, fname, buf, blen);
 
 	let ps: parser;
-	parserinit(&ps, ar, &l);
+	parserinit(&ps, &l);
 	let f: *node = parsefile(&ps);
 	// Gate cgen on parse-stage errors. Mirrors cmd/w6c/main.c's
 	// `if (l.errs || p.errs) return 1;` — broken AST otherwise reaches
@@ -160,14 +158,14 @@ export fn main(argc: i32, argv: **u8) i32 = {
 	// enum↔int reinterpret, #53 N_BLOCK scoping, #55 nominal-first variant
 	// compare, #56 bare-leaf same-module preference.
 	let tc: tctx;
-	typesinit(&tc, ar);
+	typesinit(&tc);
 	let ck: checker;
-	checkinit(&ck, ar, &tc);
+	checkinit(&ck, &tc);
 	checkfile(&ck, f);
 	if (ck.errs > 0) { return 1; };
 
 	let cg: cgen;
-	cgeninit(&cg, ar);
+	cgeninit(&cg);
 	cgfile(&cg, f);
 	return 0;
 };