nessa: retire the API copy now served by nessa-api.freno.me

The Nessa API (nessaDb.*, nessa.community.*, Clerk auth and the Clerk user
webhook) lives in the Nessa repo's server/ on pan. This copy never served
the app: RemoteAPIClient wraps every input in {"input": …}, which the stock
tRPC adapter here reads as the input itself (queries 404, writes no-op).
Clerk's webhook already targets nessa-api.freno.me.

Drops the routers, nessa-auth, the webhook, NessaConnectionFactory, the
NESSA_* env and the now-unused @clerk/backend and svix. Nessa's marketing,
privacy and deletion pages stay.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/server/api/routers/misc.test.ts

@@ -137,7 +137,7 @@ describe("p8-001 / p8-008 static source audit", () => {
     it(`${proc} is not declared as publicProcedure`, () => {
       // Match the procedure declaration line and ensure it is not publicProcedure.
       const re = new RegExp(
-        `\\b${proc}\\s*:\\s*(publicProcedure|csrfProtectedProcedure|protectedProcedure|adminProcedure|nessaProcedure)`
+        `\\b${proc}\\s*:\\s*(publicProcedure|csrfProtectedProcedure|protectedProcedure|adminProcedure)`
       );
       const m = SOURCE.match(re);
       expect(m, `${proc} declaration not found`).not.toBeNull();