Add `sqitch grep` command.

[Ovid]

After a nail-biting five years of anticipation, here's the pull request for sqitch grep.

Full tests and documentation included.

Name
    sqitch-grep - Search change scripts and display results in plan order

Synopsis
      sqitch grep [options] <search-term> [<search-term> ...]
      sqitch grep ALTER TABLE
      sqitch grep --type deploy "CREATE INDEX"
      sqitch grep --insensitive --list "drop table"
      sqitch grep --regex "foo.*bar"

sqitch help grep will give full information.

Disclaimer: while the grep.pm code is based on the code I wrote several years ago, the tests and the documentation have been written by Amazon's Kiro using Claude Sonnet 4.5.

[theory]

Thanks for the PR. If you don't mind:

• Please squash this down to a single commit
• Remove all AI junk: reviews, unreviewed code

Thanks!

[Ovid]

• Remove all AI junk: reviews, unreviewed code

What does this mean? Do you want me to remove the reviews on this page? Happy to squash to a single commit, but I'm unsure of what you're asking above.

[Ovid]

@theory I've gone through the code with a fine-toothed comb. I've made a few minor changes here and there, but largely stylistic (but added some missing POD). I've squashed it all to a single commit.

Is there more you'd like me to take care of?

[Ovid]

Also, I listed you as the author on grep.pm. Wasn't sure if there's guidance on that, but happy to have your name there.

[theory]

What does this mean? Do you want me to remove the reviews on this page? Happy to squash to a single commit, but I'm unsure of what you're asking above.

I tried to delete the LLM comments, but got an error; I've reported the bug to GitHub. If you can remove them, great! But I assume this PR is stuck with them.

No, what I meant is that all the generated code needs to be exactly like all the other code in the project, and if it's not, should be removed and replaced or refactored, as appropriate. I trust you, not code generators.

Er, and it sounds like you've already done that. 🤦🏻 I'll review sometime this week, I hope.

Don't worry about the CI failures, BTW; something's broken with the Windows builds and the Snowflake builds don't work for PRs from users without the permissions for the Snowflake credentials. Though I would have thought you'd have them TBH. I'll make sure those tests pass at merged time.