fix: pagination loop termination and issue de-duplication

[Codimow]

🎯 Fix: Pagination Loop Termination with Since Filter

Closes #1

Issue

Issue #1 — Pagination fails when fetching repository issues with the Since filter.

Root Causes Found

1. Wrong API Method Name (Critical — Code Did Not Compile)

The code called f.client.Issues.ListByRepository(...) which does not exist in go-github v57. The correct method is ListByRepo.

-issues, resp, err := f.client.Issues.ListByRepository(ctx, owner, repo, opt)
+issues, resp, err := f.client.Issues.ListByRepo(ctx, owner, repo, opt)

2. Missing go.sum

The repository was missing go.sum, preventing dependency resolution.

3. main.go Import Issues

The original main.go had a broken import alias and used an unauthenticated client despite requiring a GITHUB_TOKEN.

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Files Changed

File	Change
pkg/github/client.go	Fixed ListByRepository → ListByRepo, added context cancellation checks, max-page safety bound, defensive perPage default, and comprehensive documentation
pkg/github/client_test.go	Rewrote with 9 tests covering all acceptance criteria
main.go	Fixed import alias, switched to oauth2-authenticated client
go.sum	Generated via go mod tidy

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Acceptance Criteria Verification

Criteria	Status	Test
✅ Pagination retrieves all pages with Since active	PASS	TestFetchIssuesWithSincePagination
✅ Loop relies on NextPage from response, not slice length	PASS	TestFetchIssuesWithSincePagination (page 2 returns 1 item < PerPage)
✅ Since preserved across all paginated calls	PASS	TestFetchIssues_SincePreservedAcrossPages
✅ Handles empty page with NextPage link	PASS	TestFetchIssues_EmptyPageWithNextLink
✅ No duplicate issues	PASS	TestFetchIssues_NoDuplicates

Additional Quality Tests

Test	What It Covers
TestFetchIssues_SinglePage	Single-page response terminates in exactly 1 request
TestFetchIssues_RateLimit	403 rate-limit error propagated correctly
TestFetchIssues_ContextCancellation	Cancelled context returns promptly
TestFetchIssues_DefaultPerPage	perPage <= 0 defaults to 30 instead of sending invalid value
TestFetchIssues_Integration	Live API test (skipped without credentials)

All tests pass ✅ | Race detector clean ✅ | go vet clean ✅