Fix broken migration fallback in CLAUDE.md; add defensive null guards

The documented shadow-database-free fallback for generating migration SQL
(--from-migrations ... --to-schema-datamodel ...) was never actually tested
and fails for the same P3014 reason `migrate dev` does, since
--from-migrations also requires --shadow-database-url internally. Verified
against the local dev DB that --from-schema-datasource (live introspection,
no shadow DB) diffed against --to-schema-datamodel (static file read) works
in both the no-op case and a real ADD COLUMN case, and documented that
instead. Also corrected the inaccurate claim that this matched Task 3's
approach (Task 3 used --from-empty) and moved the suggested SQL output path
out of the repo root into the OS temp directory.

Also brings markFailed's errorMessage/errorLog params in line with markDone's
existing ?? null guard, and adds orderBy to findExpiredJobs to match
findPendingJobs, for consistency.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/jobs/jobRepository.js

@@ -67,7 +67,7 @@ export async function markDone(prisma, id, { outputPath, outputMimeType, outputS
 export async function markFailed(prisma, id, { errorMessage, errorLog }) {
   await prisma.conversionJob.update({
     where: { id },
-    data: { status: 'failed', errorMessage, errorLog },
+    data: { status: 'failed', errorMessage: errorMessage ?? null, errorLog: errorLog ?? null },
   });
 }
 
@@ -83,6 +83,7 @@ export async function findPendingJobs(prisma, limit) {
 export async function findExpiredJobs(prisma) {
   return prisma.conversionJob.findMany({
     where: { expiresAt: { lt: new Date() }, cleanedAt: null },
+    orderBy: { createdAt: 'asc' },
     select: jobSelect,
   });
 }