fix: bypass Next.js fetch cache for GitHub contributions API

[TanayJalan]

What this PR does

This PR fixes an issue where the user's GitHub contribution count would remain stale even after using the Loadout refresh functionality or returning to GitCity later.

Root Cause

By default, Next.js (App Router) aggressively caches fetch requests across the server, including POST requests to external APIs like the GitHub GraphQL API. Because of this, the background refresh job (refreshDeveloper) was continually receiving and saving the exact same cached contribution data from the user's initial login, rather than hitting GitHub's servers for fresh data.

Solution

• Added cache: "no-store" to the fetch call for https://api.github.com/graphql in src/lib/github-api.ts.
• Added cache: "no-store" to the repository list fetch calls in src/lib/github-api.ts and src/app/api/dev/[username]/route.ts to ensure users' repository stats are also kept strictly up to date.

This forces Next.js to bypass its internal data cache, ensuring GitCity successfully retrieves the latest GitHub data on every background refresh.

Closes #112

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