fix(github): point GitHub services at the renamed repo

[PonceGL]

What

GitHubAnnouncementPropertiesService.fetchPlayStoreAnnouncement() defaulted
to owner=theovilardo, repo=PixelPlay — the project's name before the
rename to PixelPlayerHQ/PixelPlayer. One of the small independent fixes
listed in #2813.

It works today only because raw.githubusercontent.com still resolves the
old path (verified: both URLs return identical content, same etag) — a
silent dependency on nobody claiming the old name.

Change

Points the defaults at the real repo. Single caller (MainActivity.kt) uses
no arguments, so that's the only thing that needed to change there.

A self-review pass (before this PR went up) found the identical problem in
the sibling GitHubContributorService.fetchContributors(), same
owner/repo defaults, powering the About screen's contributor list
(also called with no arguments) — not named in the original plan, but the
same bug. Confirmed empirically that this one is worse than the announcement
case: unlike the raw-content path, api.github.com/repos/theovilardo/PixelPlay
returns an actual HTTP 301, not a silent 200. Fixed with the same
one-line-per-default change.

Testing

No test added in either file — this predates a separate, unmerged branch
that genericizes GitHubAnnouncementPropertiesService in a way that makes
it testable without hitting real network; redoing that refactor here would
duplicate that branch's own scope, and GitHubContributorService has no
equivalent seam at all. Nothing to assert about a default string value
without one.

assembleDebug succeeds, full JVM baseline unaffected (5 pre-existing
failures, none new).

[PonceGL]

Closing for now — reorganizing how this work is staged. It'll go through our fork first and we'll propose it upstream again, possibly bundled differently, once the larger feature it's part of is further along. Not a rejection, just a process change on our side.