docs: correct the summary job's log group path

[hughgrigg]

The "When a run fails" section sent a reader to /aws/lambda/<function>, where nothing is written. SummaryFunction passes the Function an explicit LogGroup carrying no logGroupName, and CloudFormation therefore names the group after the stack and the logical id, the way the permissions section further down already says it names the function and the roles. Somebody following the old line looked in an absent log group while a run was failing. The bullet now claims only what it can, and a paragraph under it gives the name's shape, says the /aws/lambda path holds nothing here, and points at the function's Monitor tab in the console and a describe-stack-resources query for a terminal. Naming the group conventionally was the other end to fix, and it was left alone. The log group is passed into the function, so deriving its name from the function's Ref is a CloudFormation cycle, and the physical function name that breaks the cycle would be a fourth name needing to be unique per account, beside schedulePrefix, workgroupName and databaseName. Documentation only, and no construct changes.

pnpm check fails on main at src/cdk/rollup-summaries.test.ts:539, where viewsOnly is undefined and two tests throw on it. That arrived with #91 and is unrelated to this branch. The box below is unticked for it, and every other step of the check passes here.

@coderabbitai ignore

• Conventional commit message, used as the title

• Conventional branch name, like feat/concise-description

• Full check with pnpm run check passed

• Rebased off latest main

• User-facing behaviour is documented in docs/

See https://www.conventionalcommits.org/en/v1.0.0/