fix(ci): build Hypatia escript from repo root in dogfood gate

The hypatia repo no longer has a scanner/ subdirectory — mix.exs and
hypatia-cli.sh now live at the repo root. The dogfood build step still
did `cd scanner && mix escript.build`, which failed with
'cd: scanner: No such file or directory' and red-flagged every PR
(pre-existing on main; surfaced as a blocking red here).

Build from the root and use the canonical `hypatia` escript name
(hypatia-cli.sh already prefers it over legacy `hypatia-v2`).

Refs verisimiser#59

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: hyperpolymath

.github/workflows/hypatia-scan.yml

@@ -48,8 +48,13 @@ jobs:
       - name: Build Hypatia scanner
         run: |
           cd "$HOME/hypatia"
-          if [ ! -f hypatia-v2 ]; then
-            cd scanner && mix deps.get && mix escript.build && mv hypatia ../hypatia-v2
+          # The Hypatia scanner is an escript built from the repo root
+          # (mix.exs and hypatia-cli.sh live at the root; there is no
+          # longer a scanner/ subdirectory). `mix escript.build` produces
+          # `hypatia`, which hypatia-cli.sh prefers over the legacy
+          # `hypatia-v2` name, so no rename is needed.
+          if [ ! -f hypatia ]; then
+            mix deps.get && mix escript.build
           fi
 
       - name: Run Hypatia scan