chore(repo): archive historical docs under Docs/archive, drop tracked pycache

Move closed audits, task briefs, design rounds, perf reports, the OPSTACK
plan/progress logs and WORK-NEXT.md into Docs/archive/ (git mv, history kept).
Whitelist Docs/ in the strict .gitignore, ignore Tools/**/__pycache__/, and
remove the tracked .pyc. Repoint references in the kept docs and in non-test
source comments to the new paths.

Source/VoxelForge/VoxelForge.Build.cs

@@ -26,7 +26,7 @@ public class VoxelForge : ModuleRules
 		//
 		// Precise resolves to "/fp:precise" on MSVC and "-ffp-contract=off" on Clang — both
 		// IEEE-754 compliant with no FMA contraction, so the two toolchains agree BY CONSTRUCTION
-		// rather than by luck. That is the fix for AUDIT-2026-07.md C9.
+		// rather than by luck. That is the fix for Docs/archive/AUDIT-2026-07.md C9.
 		//
 		// COST: /fp:precise forbids the reassociation and contraction /fp:fast allowed, on a
 		// noise-heavy hot path. Expect a measurable perf regression and check it against