Honor account country when applying geo media and legal takedown rules

[Pitchfork-and-Torch]

Bug

DropTweetsWithGeoRestrictedMediaRule calls media_restricted_in_viewer_country. That helper reads only request country_code and treats a missing value as xx (worldwide). ViewerPredicates.country() already prefers account_country_code, then request country.

A US-account viewer with no request country is dropped from US allow-listed media on TimelineHomeRecommendations. Legal/local takedown helpers had the same request-only hole.

This is not safety-label applicable_countries (PR 110). Media geo lists and takedown reasons are a different object.

Fix

Resolve viewer country as account_country_code, then country_code, then xx for media. Legal/local takedown uses the same account-then-request pair. Missing both still drops allow-listed media (existing unknown-country case).

Proof

• Entry: media geo_allow_list / geo_deny_list; takedown_reasons
• Sink: DropTweetsWithGeoRestrictedMediaRule / legal takedown Drops
• Break: request country_code only; account country ignored
• Viewer effect: US-account viewer, no request country, US allow-listed video disappears from For You
• Twin: ViewerPredicates.country() already prefers account_country_code

Tests

• geo_allow_listed_media_allows_account_country_when_request_country_missing (fails on unmodified main)
• geo_denied_media_drops_account_country_oon
• geo_allow_listed_media_drops_unknown_country_oon still drops when both countries are missing
• unit tests added; cargo test cannot run in the public dump