Add evolution chain navigation with e/E keys

[rae89]

Summary

• Decouple evolution chain fetching from load_detail so left/right arrow navigation stays fast — chain loads asynchronously after detail arrives
• Add e/E keybindings to navigate forward/backward through the evolution chain with wrap-around
• Add evolution_chain_species() helper to flatten chains (including branching ones like Eevee) into a navigable species list
• Update detail view help text to show [←→] Nav and [e/E] Evo keybindings

Refactor

• Extract duplicate capitalize() from 3 UI files into shared pub fn in ui/mod.rs
• Consolidate filtered_list() and modal_filtered_list() via shared filter_pokemon_list(query) method
• Have App::new() delegate to new_with_team_data() to eliminate 30 lines of duplicated field initialization
• Add test_summary(), test_detail(), test_pokemon_list() test helpers to reduce boilerplate (~400 lines removed)
• Simplify evolution chain test construction using make_chain() helper

Test plan

• cargo build passes
• cargo test — all 101 tests pass
• cargo clippy — no warnings
• Run TUI: Left/Right arrows navigate filtered list (same speed as before)
• Run TUI: Press e on Bulbasaur → loads Ivysaur → e → Venusaur → e → wraps to Bulbasaur
• Run TUI: Press E goes backward through the chain
• Edge cases: single-stage Pokemon (e/E does nothing), Eevee (navigates through all eeveelutions)

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