Migrate from v1

V1 and v2 remain separate references.

The v2 base path is /v2, not /api/v2.

v1	v2
`GET /api/v1/public/discord-to-roblox`	`GET /v2/discord`
`GET /api/v1/public/roblox-to-discord`	`GET /v2/roblox`
`GET /api/v1/public/detections/alt`	`GET /v2/alts`
`POST /api/v1/verify/session`	`POST /v2/sessions`

V1 link writes use query parameters; v2 writes use JSON bodies. V1 session fields such as sid and status_reason become id and statusReason. V1 SSE uses status, complete, and expired; v2 emits session events.