fix(www): guard github/discord counters against invalid API responses

[Yeom-JinHo]

Description

This PR updates the social counter components in www to prevent runtime failures when external API responses are invalid or unavailable.

It adds defensive parsing and fallback handling for both GitHub stars and Discord online member counts.

Changes

• Added safe count format helper (formatCompactCount) in:
  • apps/www/components/github-link.tsx
  • apps/www/components/discord-link.tsx
• Refactored GitHub stars fetch logic into getStarsCount() with guards:
  • Returns 0 when fetch fails
  • Returns 0 when response is not ok
  • Returns 0 when payload shape is invalid (stargazers_count missing/non-numeric)
• Refactored Discord member fetch logic into getActiveMembersCount() with guards:
  • Returns 0 when fetch fails
  • Returns 0 when response is not ok
  • Returns 0 when payload shape is invalid (presence_count missing/non-numeric)
• Updated rendering logic to use validated numeric values only, instead of directly reading raw JSON fields.

Motivation

• External APIs can return unexpected payloads (rate limits, errors, malformed responses).
• Direct toLocaleString() calls on undefined values can crash prerender/build.
• This change ensures stable rendering and safe fallback behavior for social counters.

Breaking Changes

• None.

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