fix: standardize username to 'football' in all hooks (FINDING-008)

The preseed.cfg creates user 'football' but hooks referenced 'kneluser'.
This inconsistency would cause runtime failures during installation.

Changes:
- config/hooks/installed/encryption-validation.sh: s/kneluser/football/g
- config/hooks/live/usb-automount.sh: s/kneluser/football/g
- config/hooks/installed/install-scripts.sh: s/kneluser/football/g
- tests/unit/encryption-validation_test.bats: Add 5 tests for username consistency

Fixes: FINDING-008 (User account inconsistency)
Reference: PRD.md user account requirements

💘 Generated with Crush

Assisted-by: Claude via Crush <crush@charm.land>

tests/unit/encryption-validation_test.bats

@@ -18,3 +18,32 @@
 @test "Validation script uses set -e for error handling" {
     grep -q "set -e" /workspace/config/hooks/installed/encryption-validation.sh
 }
+
+# =============================================================================
+# USERNAME CONSISTENCY (FINDING-008)
+# =============================================================================
+
+@test "Username 'football' is consistent across all hook files" {
+    # preseed.cfg creates user 'football', hooks should reference same username
+    run grep -r "kneluser" /workspace/config/hooks/
+    [ "$status" -ne 0 ]
+}
+
+@test "Username in preseed.cfg is 'football'" {
+    grep -q "passwd/username string football" /workspace/config/includes.installer/preseed.cfg
+}
+
+@test "encryption-validation.sh uses correct username 'football'" {
+    # Should NOT reference 'kneluser'
+    ! grep -q "kneluser" /workspace/config/hooks/installed/encryption-validation.sh
+}
+
+@test "usb-automount.sh uses correct username 'football'" {
+    # Should NOT reference 'kneluser'
+    ! grep -q "kneluser" /workspace/config/hooks/live/usb-automount.sh
+}
+
+@test "install-scripts.sh uses correct username 'football'" {
+    # Should NOT reference 'kneluser'
+    ! grep -q "kneluser" /workspace/config/hooks/installed/install-scripts.sh
+}