fix: resolve SonarQube S1192 and S3776 issues in discussions.go

[devin-ai-integration]

Closes: SonarQube issues go:S1192 (String literals should not be duplicated) and go:S3776 (Cognitive Complexity too high) in pkg/github/discussions.go.

Summary

Addresses two High-severity SonarQube findings in discussions.go, scoped to a single file change:

S1192 – Duplicated string literals: Extracted four repeatedly-used literals into package-level constants (descRepoOwner, descRepoName, errGQLClientFmt, categoryLabelFmt). Each was duplicated 3–4× across the four tool functions in this file.

S3776 – Cognitive Complexity of ListDiscussions (27 → well under 15): The original function contained two near-identical branches (with/without category filter), each with inline struct definitions, query execution, and node-to-Issue mapping. Refactored by extracting:

• discussionNode – shared struct type for GraphQL response nodes
• queryDiscussionsWithCategory / queryDiscussionsWithoutCategory – query helpers
• mapDiscussionNodesToIssues – shared mapping logic

Important review items

1. Behavioral change on empty results: The original code returned null JSON when no discussions were found (nil slice via var discussions []*github.Issue). The new code returns [] (empty slice via make). This is arguably more correct but is a subtle contract change worth verifying downstream consumers can handle.
2. GraphQL struct tag propagation: Confirm the extracted discussionNode type with its graphql:"category" and graphql:"url" tags is correctly resolved by the githubv4 client when used inside the wrapper query structs in queryDiscussionsWithCategory/queryDiscussionsWithoutCategory.
3. Constant naming scope: descRepoOwner, descRepoName, etc. are unexported (lowercase) and local to the github package. If other files in this package use the same literals, these constants could be reused — but this PR intentionally limits changes to one file.

Tradeoffs

• Two separate query helper functions (queryDiscussionsWithCategory / queryDiscussionsWithoutCategory) were kept instead of a single parameterized function because the GraphQL query struct tags differ (discussions(first: 100, categoryId: $categoryId) vs discussions(first: 100)), making compile-time struct unification non-trivial.

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Link to Devin run: https://app.devin.ai/sessions/cb8670bcf6e74341a4ed0784765549ec
Requested by: Shannon Hittson (@shannonhittson-eng)

[devin-ai-integration]

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[sonarqubecloud]

Quality Gate passed

Issues
7 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
2.2% Duplication on New Code

See analysis details on SonarQube Cloud