Fix #1: Add support for spacer items in flex layouts

[cassdeckard]

Summary

Implements fix for #1: adds support for spacer items in flex containers so layouts can "float" primitives (e.g. a form) to the right by consuming remaining space on the left.

Changes

• Config: Added spacer: true field to FlexItem in config/types.go
• Builder: Updated buildFlex and populateFlexItems in builder/builder.go to treat primitive: null or spacer: true as spacers—call flex.AddItem(nil, item.FixedSize, item.Proportion, item.Focus) instead of skipping
• Demos:
  • nested-pages-example.yaml: Added spacer between textView and form to float form right (fixedSize 55)
  • flex.yaml: Added spacer for acceptance test (Flex page is reliably navigable)
• Tests:
  • Unit: TestBuildFlex_SpacerItems, TestBuildFlex_SpacerFlag in builder/builder_test.go
  • Acceptance: TestAcceptance_SpacerLayout navigates to Flex page and asserts snapshot

Usage

items:
  - primitive:
      type: textView
      text: "Left"
    fixedSize: 10
    focus: false
  - primitive: null   # spacer - consumes remaining width
    proportion: 1
    focus: false
  - primitive:
      type: form
      formItems: [...]
    fixedSize: 55
    focus: true

Alternative: spacer: true on a flex item.

Testing

• go test ./... (library tests pass)
• cd example && go test -run TestAcceptance_SpacerLayout -v ./... (acceptance test passes)
• cd example && go test -run TestAcceptance_Layout -v ./... (layout tests pass)

[github-actions]

Test Results

243 tests  +2   243 ✅ +2   0s ⏱️ ±0s
  5 suites ±0     0 💤 ±0 
  1 files   ±0     0 ❌ ±0 

Results for commit 9df3038. ± Comparison against base commit 284b19f.

♻️ This comment has been updated with latest results.