types: restore Supabase row typing, fix parseInput inference (586→76 tsc errors)

The installed supabase-js (2.99, 5 generics) is incompatible with
@supabase/ssr@0.6.1 (calls it with 3), collapsing the server client's
schema to `never` — the root cause of ~450 of the 586 hidden type errors
(next.config typescript.ignoreBuildErrors masks them all).

- lib/supabase/server.ts: annotate the factory as SupabaseClient<Database>
  and bridge the ssr/js impedance mismatch at the one documented boundary;
  type the setAll cookie params.
- lib/supabase/proxy.ts, proxy.ts: type the setAll cookie params.
- lib/auth-helpers.ts: parseInput now infers its result from the schema via
  z.infer (was a fragile ZodSchema<T> that widened outputs to {}).
- lib/validations.ts: annotate flexibleDateTime's output type.
- types/database.ts: add class_signup_tx / class_cancel_tx RPC signatures
  (called but absent; pending full regeneration).
- tsconfig.json: target ES2020 (door-log-logic uses BigInt literals).
- vitest.setup.ts: import beforeAll/afterAll instead of relying on globals.

No runtime behavior change; 639 tests still green. ignoreBuildErrors stays
on until the remaining errors reach zero.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

types/database.ts

@@ -1702,6 +1702,16 @@ export type Database = {
         Args: { sid: string; perm: string }
         Returns: { member_id: string }[]
       }
+      // Hand-added to match scripts/045_class_signup_concurrency.sql until this
+      // file is regenerated from the live schema (`supabase gen types typescript`).
+      class_signup_tx: {
+        Args: { p_session_id: string; p_space_id: string; p_member_id: string }
+        Returns: { signup_id: string | null; signup_status: string | null; err: string | null }[]
+      }
+      class_cancel_tx: {
+        Args: { p_session_id: string; p_space_id: string; p_member_id: string }
+        Returns: { cancelled_id: string | null; promoted_id: string | null; err: string | null }[]
+      }
     }
     Enums: {
       area_lead_status: "active" | "vacant" | "handoff"