refactor: add Gap to bull_ui and drop gap dependency

[wired-pasteque]

Removes the external gap package from the project.

bull_ui now ships its own Gap (vendored from gap 3.0.1), and every feature sources Gap through bull_ui instead of importing package:gap.

[claude]

Claude finished @wired-pasteque's task in 3m 6s —— View job

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PR Review — vendoring Gap into bull_ui

• Gather context (diff vs origin/develop)
• Review vendored Gap implementation against gap 3.0.1
• Check import rewiring for leftovers/regressions
• Verify pubspec/dependency cleanup
• Post review findings

Summary: no correctness bugs, security issues, or regressions found. The vendored implementation is behaviorally identical to upstream gap 3.0.1, and the 250+ import swaps are clean and mechanical. Two minor, non-blocking suggestions below.

(Note: I can't submit formal inline review comments, so findings are consolidated here with file/line references.)

What I verified

• Vendored code fidelity (packages/bull_ui/lib/src/layout/gap.dart): compared Gap, _RawGap, and RenderGap against upstream 3.0.1 — constructors and asserts, the Scrollable.maybeOf fallback (the fix that 3.0.1 introduced), the RenderFlex direction lookup, intrinsic sizing, computeDryLayout/performLayout, the color paint path, and the markNeedsLayout/markNeedsPaint setters all match. The only changes are cosmetic (super-parameters, doc comments), as the header claims.
• No leftovers: zero remaining package:gap references in code, tests, or any pubspec; gap is removed from root pubspec.yaml, packages/bull_ui/pubspec.yaml, and pubspec.lock consistently. MaxGap/SliverGap are confirmed unused in the repo, so dropping them loses nothing.
• Import swaps: app code uses import 'package:bull_ui/bull_ui.dart' show Gap;, which is a good call — it avoids pulling bull_ui's broad Material re-exports into scope of ~250 files. bull_ui internals correctly use the direct src/layout/gap.dart import. I checked for duplicate bull_ui imports introduced by the swap and found none. bull_ui.dart exports only Gap (not RenderGap), which nothing else needs.

Minor suggestions (non-blocking)

1. License text (packages/bull_ui/lib/src/layout/gap.dart:3): the header credits the author and names the MIT license, but MIT's condition is that the full license text accompany substantial copies. Consider pasting the full MIT text into the header or adding a third-party-notices entry. Fix this →
2. Test coverage: packages/bull_ui/test/ has widget tests for the other components but none for the vendored Gap. Now that the code is owned in-repo, porting upstream's small test suite (sizing in Row/Column, the Scrollable fallback, the error when no direction is resolvable) would guard the vendored copy against future edits. Fix this →

One caveat: this runner has no Flutter SDK, so I couldn't run flutter analyze/flutter test — the existing CI checks should confirm compilation.