Make Sprocket the source of truth for player identity and platform accounts

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Summary

Make Sprocket authoritative for player identity, Discord linkage, platform accounts, and tracker links, rather than relying on mledb.player, mledb.player_account, and bridge rows.

Why

Active roster/admin workflows still dual-write identity and account data into MLEDB. That keeps legacy tables in the critical path for account reporting, player creation, and player lookup.

Relevant code

• core/src/franchise/player/player.service.ts
• core/src/organization/member/member.mod.resolver.ts
• core/src/mledb/mledb-player-account/mledb-player-account.service.ts
• core/src/mledb/mledb-player/mledb-player.service.ts

Scope

• Finalize the Sprocket-owned model for player identity and external platform accounts.
• Ensure Discord linkage, tracker links, and platform account ownership can be fully resolved from Sprocket.
• Preserve legacy ID crosswalk fields only where they are still needed for migration/cutover.
• Update active write paths so Sprocket becomes the primary write target.
• Limit legacy mirroring to a temporary compatibility mechanism, if still required.

Acceptance criteria

• New and updated player/account records can be fully reconstructed from Sprocket alone.
• Active account-reporting flows succeed without depending on legacy-only data structures.
• The set of fields still mirrored into MLEDB is explicitly documented and minimized.
• There is a clear removal plan for mledb.player_account writes.