ci: rename build-nsInnoUnp.yml -> build-ns7zip.yml; update doc refs

Workflow now targets Simone/nsis-plugin-ns7zip. Renamed the file and
the workflow `name:`, and updated all references in active docs
(plans/archived and docs/archived left as frozen history).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.gitea/workflows/build-ns7zip.yml

@@ -1,4 +1,4 @@
-# Build (Local CI) — pipeline per nsis-plugin-ns7zip
+# Build ns7zip (Local CI) — pipeline per nsis-plugin-ns7zip
 #
 # Cross-platform matrix build: runs in parallel on both windows-build (WinRM)
 # and linux-build (SSH) runners using the reusable composite action.
@@ -6,7 +6,7 @@
 #
 # Trigger: push su tag v*, oppure run manuale
 
-name: Build (Local CI)
+name: Build ns7zip (Local CI)
 
 on:
   push: