docs(tools): tripwire the stale pulsar-parvagues-hud copy against pre-gig backwards fixes

tools/pulsar-parvagues-hud/README-STALE.md

+# STALE COPY — do not "fix" this
+
+This copy of `pulsar-parvagues-hud` is stale (v0.1.0-era, 183-line `main.js`).
+The live package Pulsar actually loads is:
+
+- Path: `/home/pln/.pulsar/packages/pulsar-parvagues-hud`
+- Version: v0.2.0 (514-line `lib/main.js`, plus `scenes.js`, `render.js`,
+  `desk-silence.js`, `eval-publish.js`, …)
+
+Do NOT edit this tree, and do not copy anything from it into the installed
+package — that would be a backwards fix. Everything you may want to change
+belongs in the installed package above. Kept in place only for git history
+stability. (Pre-gig note for the Thu 24 gig.)