fix(ci): build Hypatia escript from repo root (estate dogfood drift)

The hypatia repo dropped its scanner/ subdirectory; mix.exs now lives at
the repo root. The dogfood build step still did `cd scanner`, failing with
"cd: scanner: No such file or directory" and red-flagging every PR.
Build from the checkout root instead. Idempotent estate sweep.

Refs verisimiser#59

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

Author: hyperpolymath

.github/workflows/static-analysis-gate.yml

@@ -146,7 +146,6 @@ jobs:
           if [ -d "$HOME/hypatia/scanner" ]; then
             cd "$HOME/hypatia"
             if [ ! -f hypatia-v2 ]; then
-              cd scanner
               mix deps.get
               mix escript.build
               mv hypatia ../hypatia-v2