Enforce make lint in CI - #1907

Stacked on #1906 (which is stacked on #1905). Review those first; this PR targets #1906's branch.

The problem

make lint fails on main:

$ swiftformat --lint .
Source input did not pass lint check.
46/125 files require formatting.

25 of those are in Sources, 13 in the example, 7 in Tests, and one is Dangerfile.swift.

Nothing ever ran it. There are workflows for the tests, the framework, the example app, and Danger — but none for lint, so the drift from the repo's own .swiftformat grew unchecked. Some of it is not cosmetic: AppDelegate.swift and AdvancedExampleViewController.swift had genuinely misindented lines.

The change

Two parts:

1. A Lint workflow that installs SwiftFormat and SwiftLint and runs make lint on every PR.
2. The formatting that workflow then demands, so it starts green.

The second part is the whole 46-file diff. It is swiftformat . output and nothing else — no hand edits. Almost all of it is two rules:

• organizeDeclarations moving members into the configured order
• redundantSelf dropping explicit self.

SwiftLint already passed and needed no changes.

Reviewing this

The diff is large but mechanical. To confirm it is only formatting, check out the branch and run swiftformat . on the parent commit — the result should be identical.

Verification

• make lint exits 0.
• MessageKit unit tests: 60 of 60 pass on an iPhone 17 simulator (iOS 27).
• The example app builds, and its unit and UI tests pass.

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