[#330] Add RLS SELECT policies for trade_history tables

[realproject7]

Context

trade_history, backfill_failures, and backfill_cursor tables have RLS enabled but no SELECT policy. The browser-side anon Supabase client returns empty arrays, which breaks the PriceChart component.

Scope

Create migration supabase/migrations/00018_rls_public_read.sql:

-- trade_history: public read for price charts
create policy "Public read" on public.trade_history for select using (true);

-- backfill_failures: public read for diagnostics
create policy "Public read" on public.backfill_failures for select using (true);

-- backfill_cursor: public read for status checks
create policy "Public read" on public.backfill_cursor for select using (true);

Acceptance Criteria

• Migration file created and applies cleanly
• npm run typecheck passes
• PriceChart shows trade data when trade_history has rows

Labels

agent/T3