refactor(explore): split explore_screen.dart by tab

[realmeylisdev]

Source audit context: origin/main at commit 1be7b7790 (2026-05-18). Filed as a child of #4339 per the ratification thread.

Severity

Medium

Problem

mobile/lib/screens/explore_screen.dart (1,276 lines, 26 commits in last 90 days) holds the explore screen with all its tabs (trending, popular, search, hashtags), tab-state coordination, and feed-wiring logic in one widget.

Evidence

• 1,276 lines, 26 commits in the last 90 days.

Impact

Medium. Common file for explore-feature work; tab-level changes have to reason about the whole screen.

Recommended fix

Extract each tab into its own page widget under mobile/lib/screens/explore/tabs/. Coordinate via ExploreTabsCubit. Parent becomes a thin tabs scaffold.

Acceptance criteria

• Parent screen under 400 lines.
• Each tab file is under 500 lines.

Related

• Parent epic: epic(maintainability): reduce oversized files, complexity, and general code drag #4339
• Related: refactor(router): retire forceExploreTabNameProvider after /explore/tab/:name rollout #4123 (retire forceExploreTabNameProvider) — recommend co-sequencing.