refactor(checkbox): share regex literals via exported storage vars

[bborbe]

Summary

PR #36 broadened the checkbox regex to accept * list markers, but the pattern (and its two replacement variants) were duplicated across 7 inline sites in pkg/storage and pkg/ops. This refactor centralizes them as three exported package-level vars in pkg/storage:

• storage.CheckboxRegex — detection (^(\s*)[-*] \[([ x/])\] (.+)$)
• storage.CheckboxCompleteRegex — rewrite [ ] / [/] → [x] preserving marker
• storage.CheckboxUncompleteRegex — rewrite [x] → [ ] preserving marker

pkg/ops/{complete,update,workon}.go drop their regexp imports entirely; pkg/ops/defer.go keeps it for regexp.MatchString on an unrelated path.

Per go-package-layout-guide.md, no new sub-package — promoted in place in pkg/storage (none of the 5 split triggers fire). The 3 new exported names are the only public API delta.

pkg/ops/lint.go lines 460 and 771 intentionally untouched — they use a different state class ([ xX]) by design.

Test plan

• go test ./pkg/storage/... ./pkg/ops/... exits 0 (existing PR fix(parser): accept asterisk list-marker on checkbox regex #36 coverage exercises both dash and asterisk forms)
• git grep -nE 'storage\.CheckboxRegex' pkg/ops/ returns 4 matches; storage.CheckboxCompleteRegex and storage.CheckboxUncompleteRegex each 1
• No regexp.MustCompile.*\[-\*\] remaining in pkg/ops/
• make precommit exits 0
• git diff origin/master..HEAD -- pkg/ops/lint.go is empty

[ben-s-pull-request-reviewer]

Based on my analysis, here's my review:

Verification of all concerns from the plan:

Concern	Status
pkg/storage/base.go - three exported vars added	✅ Verified: CheckboxRegex, CheckboxCompleteRegex, CheckboxUncompleteRegex at lines 30-39
pkg/ops/complete.go - regexp import removed	✅ Verified: no regexp references, uses storage.CheckboxRegex, storage.CheckboxCompleteRegex, storage.CheckboxUncompleteRegex
pkg/ops/defer.go - regexp import retained at line 87	✅ Verified: import present, regexp.MatchString used for +Nd shorthand (unrelated to checkbox)
pkg/ops/update.go - regexp import removed	✅ Verified: no regexp references, uses storage.CheckboxRegex at line 151
pkg/ops/workon.go - regexp import removed	✅ Verified: no regexp references, uses storage.CheckboxRegex at line 244
pkg/ops/lint.go - untouched, different [ xX] regex	✅ Verified: lines 460/771 use (?m)^[\s]*[-*]\s+\[([ xX])\] (intentionally different - matches uppercase X)
CHANGELOG.md - updated	✅ Verified: line 13 documents the refactor accurately
prompts/completed/148-...md exists	✅ Verified: file exists with 260 lines

No issues found. The refactor is clean:

• Regex literals are byte-for-byte identical to the replaced inline patterns
• Import hygiene is correct across all files
• lint.go's intentionally different [ xX] state-class regexes are preserved
• The changelog accurately describes the scope

{
  "verdict": "approve",
  "summary": "Refactor is clean and correct. Three exported regex vars in pkg/storage/base.go correctly replace seven inline regexp.MustCompile call sites across pkg/ops/{complete,defer,update,workon}.go. Import hygiene verified: complete/update/workon correctly drop regexp import; defer retains it only for the +Nd shorthand at line 87. lint.go's intentionally different [ xX] regex shape at lines 460 and 771 is correctly untouched. CHANGELOG entry is accurate.",
  "comments": [],
  "concerns_addressed": [
    "correctness: pkg/storage/base.go exports CheckboxRegex, CheckboxCompleteRegex, CheckboxUncompleteRegex - byte-for-byte identical to replaced inline patterns",
    "correctness: pkg/ops/complete.go regexp import removed - no other regexp usage",
    "correctness: pkg/ops/defer.go regexp import retained at line 87 for +Nd shorthand",
    "correctness: pkg/ops/update.go regexp import removed - no other regexp usage",
    "correctness: pkg/ops/workon.go regexp import removed - no other regexp usage",
    "correctness: pkg/ops/lint.go untouched - intentionally different [ xX] regex at lines 460 and 771 preserved",
    "tests: existing test suites cover both dash and asterisk forms (PR #36)"
  ]
}