chore(r2-12): remove 7 orphaned proprietary AVEVA DLLs from lib/ (07/U-5)

Zero-reference proof passed: no *.csproj/*.props/*.targets/*.slnx names any
of the 7 binaries; no <HintPath> element exists repo-wide. Build clean after
removal. Added lib/ to .gitignore to block re-introduction.

Out of scope: purging these from git *history* (BFG/filter-repo) is a separate,
heavier decision that rewrites every clone; this removes them from the tip only.

.gitignore

@@ -51,3 +51,6 @@ src/Server/ZB.MOM.WW.OtOpcUa.Host/pki/
 
 # Documentation audit scratch dir (untracked worktree)
 .docs-audit/
+
+# Vendor binaries — never commit (license risk; see R2-12/U-5)
+lib/