Add alpha inventory and equipment UI flow

[JOY]

Source

• docs/design/45-inventory-and-equipment-system.md
• docs/design/99-alpha-gate-loot-pickup-and-salvage-placement-rules.md
• docs/design/124-alpha-inventory-equipment-ui-flow-builder-brief.md
• docs/design/45-alpha-backlog-execution-packets.md
• docs/playtests/_templates/inventory-equipment-ui/README.md
• ROADMAP.md inventory alpha item

Goal

Build the player-facing alpha inventory and equipment UI on top of the already merged server-owned inventory RPC slice.

Scope

• Body carry list with category tabs and controller-friendly focus order.
• Equipment paper doll using the canonical D4-like slots: helm, chest, gloves, pants, boots, amulet, ring_1, ring_2, main_hand, off_hand, and two_hand.
• Equipment slot evidence using docs/playtests/_templates/inventory-equipment-ui/equipment-slot-manifest.md.
• Focus order evidence using docs/playtests/_templates/inventory-equipment-ui/focus-order-note.md.
• Lock reason copy evidence using docs/playtests/_templates/inventory-equipment-ui/lock-reason-copy-note.md.
• Compare/equip flow that reads server-computed deltas and server-provided lock reasons.
• Pickup prompt and temporary Gate loot tray, including prompt-priority and Extract to keep it evidence from doc 99.
• Garden stash access.
• Salvage confirmation using server preview/result data.
• Death recap inventory section showing lost, saved, and recoverable inventory state.

Acceptance

• Unity does not compute inventory authority locally.
• All mutation requests go through Nakama RPCs.
• The UI can explain why an item cannot equip or move using player-facing copy near the failed action.
• Keyboard/controller focus can reach carry list, category tabs, equipment slots, compare actions, temporary loot, stash, salvage, death recap, and close/back controls without trapping focus.
• Two-hand/main-hand/off-hand conflict is server-owned or explicitly marked not implemented.
• Proof/objective prompt is visually distinct from normal loot prompt.
• Play Mode smoke records body carry, equipment slots, focus order, lock reason copy, compare/equip, temporary loot tray, stash, salvage, death recap, and proof/loot prompt-priority evidence.

Cut Line

No marketplace, trading, paid stash tabs, final item art, or production NFT escrow mutation in this issue. Do not close #218 until canonical slots, server-owned equip rejection, focus order, and lock-reason copy are proved or explicitly split into a follow-up issue.

[JOY]

Docs/handoff cleanup is merged via PR #227.

What changed for this issue:

• The GitHub issue body now uses the canonical D4-like slots: helm, chest, gloves, pants, boots, amulet, ring_1, ring_2, main_hand, off_hand, and two_hand.
• The docs now define the alpha inventory UI contract: body carry, equipment paper doll, compare/equip, temporary Gate loot tray, Relay Yard stash, salvage confirm, and death recap.
• Remaining Unity implementation still belongs to this issue. This docs PR does not close Add alpha inventory and equipment UI flow #218.

[JOY]

Added a focused #218 builder brief and evidence template so the Unity implementation does not need to re-read the full inventory bible. Source doc: docs/design/124-alpha-inventory-equipment-ui-builder-brief.md. Evidence template: docs/playtests/_templates/alpha-inventory-equipment-ui/. The brief keeps the canonical slots, server-computed compare/equip, temporary Gate loot tray, stash, salvage, death recap, prompt-priority, and authority notes in one handoff.