fix(tests): apply PR #54 R2 (CodeRabbit minor) — set -euo pipefail in 3 new fixtures

CodeRabbit caught: verify-lesson07.sh has `set -u` only at top + later
`set +e` / `set -e` wrapping around the hook call. Without errexit on
from the start, the wrapping is asymmetric — first iteration silently
continues past mktemp/python failures, second iteration onwards has
errexit ON. Iteration-dependent behavior.

Fix: standardize all 3 new fixture scripts to `set -euo pipefail`.
This makes the `set +e` / `set -e` pattern in verify-lesson07.sh
behave as intended (suppress errexit only for the hook call). Also
catches unset-variable bugs and pipe-failure shadowing in the other
two scripts.

All 3 still green locally after the change.

Refs PR #54 review #3141500203.

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

Author: sgwannabe

tests/fixtures/filled-ratio/verify-filled-ratio.sh

@@ -7,7 +7,7 @@
 #
 # Exit 0 = all cases match. Exit 1 = at least one mismatch (CI-blocking).
 
-set -u
+set -euo pipefail
 
 FIXTURES_DIR="$(cd "$(dirname "$0")" && pwd)"
 REPO_ROOT="$(cd "$FIXTURES_DIR/../../.." && pwd)"

tests/fixtures/lesson07-regression/verify-lesson07.sh

@@ -10,7 +10,7 @@
 # not on the panel composite_winner — the regression LESSON 0.7
 # warns about.
 
-set -u
+set -euo pipefail
 
 FIXTURES_DIR="$(cd "$(dirname "$0")" && pwd)"
 REPO_ROOT="$(cd "$FIXTURES_DIR/../../.." && pwd)"

tests/fixtures/normalize-constraints/verify-normalize.sh

@@ -4,7 +4,7 @@
 # For each case in cases.json, run scripts/normalize-constraints.py with
 # the input label and assert the output JSON matches expected.
 
-set -u
+set -euo pipefail
 
 FIXTURES_DIR="$(cd "$(dirname "$0")" && pwd)"
 REPO_ROOT="$(cd "$FIXTURES_DIR/../../.." && pwd)"