Redesign customize player page: two-pane layout + accurate commander tracking

[Jshewmaker]

Why

The trigger was a bug: on the customize-player page the soft keyboard appeared upside-down for players 3 & 4. Root cause — the whole page was wrapped in RotatedBox(quarterTurns: 2), but the OS keyboard can't be rotated. Rather than patch around an impossible constraint, we redesigned the screen around its real job: accurately capturing each player's commander setup so in-game commander-damage and color-identity tracking are trustworthy.

Design + plans live in docs/superpowers/.

What changed

Keyboard / orientation

• Removed per-seat rotation from the customize page. The pod uses the iPad in natural landscape (host types or passes it around; typing is rare — setup only). Keyboard is now upright for everyone.

Accurate tracking (the north star)

• New Player.background — a non-attacking second card (Background enchantment): contributes to color identity but never a commander-damage clock. Kept strictly separate from Player.partner (an attacking second commander = its own 21-damage clock).
• commanderPairingFor(Commander) auto-detects pairing from Scryfall keywords/oracle text → none | partner | background. New Commander.keywords field (mapped from Scryfall) powers it.
• Live "this game will track" preview: damage-clock count (1 for single/background, 2 for partner-type) + combined color-identity pips.
• Invariant verified end-to-end (state → bloc → save → in-game tracker): a Background never produces a partner clock.

Reuse (regular-group friendly)

• shared_preferences + CommanderLibraryRepository (device-local): recents (cap 20, dedup by oracleId) and favorites (star toggle). Interface is extensible to per-friend Firebase lists for the planned friends auto-sync.

Two-pane UI

• Left: player identity (name, first-class friend link, chosen commander(s), tracking preview, save). Right: Favorites / Recent / Search picker with adaptive default tab and an auto-detected "add partner / add background" banner.
• Hero banner shows partner or background as the second art. Removed three obsolete widgets.

Testing

• flutter analyze: no new issues (pre-existing app_ui/gallery errors untouched).
• Tests: root app 22/22, player_repository 17/17 — incl. pairing detection, model round-trips/backward-compat, recents/favorites storage, bloc behavior, and the background-vs-partner clock regression.
• Backward compatible: existing persisted players/commanders deserialize with new fields defaulting to [] / null.

Follow-ups (non-blocking, noted in final review)

• Localize the new picker/identity strings (incl. the background-mode search hint).
• Offer the specific "Partner with " partner when detected.
• A "change partner/background" affordance directly in the picker.
• Manual on-device QA of the two-pane layout was not run in this environment.

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