fix(tests): terminate find -exec and pass {} — the placeholder step was a no-op

tests/e2e/template_instantiation_test.sh ran:

    find ... -exec bash -c '
        file="$1"
        ... grep/sed over $file ...
    ' _ "$file"

Two defects in that one line:

  1. No ';' or '+' terminator, so the file does not parse (SC2067).
  2. "$file" is passed where {} belongs. $file is assigned ONLY inside the
     -exec body, so in the outer scope it is UNSET — $1 arrived empty, file=""
     and every grep/sed operated on an empty path.

⚠ The consequence is worse than a lint error: the placeholder-replacement step
SILENTLY DID NOTHING, then logged "All placeholder tokens replaced". A test
whose whole purpose is to prove instantiation worked was passing without
replacing a single token. That is a plausible cause of estate repos shipping
with literal {{project}} tokens still in their sources.

Corrected to "' _ {} \;" so find passes each matched path.

Found by an estate-wide shellcheck sweep of 5,111 scripts across 375 repos:
this identical stale copy exists in 30 repositories. rsr-template-repo's own
copy is already correct and restructured (371 lines vs the 268 here), so these
are stale duplicates that never picked up the upstream fix.

Author: hyperpolymath

tests/e2e/template_instantiation_test.sh

@@ -137,7 +137,7 @@ find "$TEST_REPO_PATH" -type f \
                 sed -i "s|$placeholder|$value|g" "$file"
             fi
         done
-    ' _ "$file"
+    ' _ {} \;
 
 log_pass "All placeholder tokens replaced"