Problem: 18 entries in the issues table were marked `fixed` with no PR
link or description, making it impossible to trace which canola PR
implemented each fix.
Solution: add canola PR links to entries where a PR exists (#73, #77,
#78, #84, #119, #138, #145, #146, #153, #171, #172), and add short
descriptions to pre-PR-era batch fixes (#578, #642, #645, #650, #673,
#690) that were committed directly before the PR workflow was
established.
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