refactor: extract evidence-matching helpers in maintainer.ts (fixes #416)

[Shiva210Jyoti]

Fixes #416

What

The flag.evidence as any → parse items → item.repo || item.repoFullName → compare repos pattern was duplicated 3 times in src/app/actions/maintainer.ts.

Changes

Added 3 helpers just above getFlaggedAccounts:

• repoFromEvidenceItem(item) — extracts repo or repoFullName as a string
• filterEvidenceItemsByRepos(flag, repos) — returns matching evidence items (needed by the response builder to sum xpDelta)
• flagTouchesRepos(flag, repos) — boolean, delegates to the above

Call sites updated

1. allowedFlags filter → return flagTouchesRepos(flag, repos);
2. Response map → const filteredItems = filterEvidenceItemsByRepos(flag, repos);
3. resolveFlaggedAccount auth check → const isAuthorized = flagTouchesRepos(flag, repos);

Notes

Pure refactor - zero behavior change. tsc, eslint, and vitest all pass.

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[Shiva210Jyoti]

@jakharmonika364 The PR is ready for your review!