fix: security hardening, validation, cache and analytics fixes

Backend security:
- Admin-gate /admin/redundancy (GET+POST) with zod validation and tool existence checks
- Restrict CORS to same-origin (plus CORS_ORIGIN allowlist) and SameSite=Lax cookie
- Validate returnTo to prevent open redirect in the OIDC flow
- Validate/coerce relations body, reject self-relations and non-admin 'recommended'
- Add central JSON error middleware (no more Express HTML 500s)
- Fail fast at startup when SESSION_SECRET/VOTER_SECRET missing in production

Backend correctness:
- Stop leaking voterToken in the create-rating response
- Allow clearing websiteUrl/iconUrl (nullable in UpdateToolBody, frontend sends null)
- Regenerate session after login/callback (session fixation) and add OIDC state check
- Block self-demotion and last-admin demotion in user PATCH
- Set created_by to NULL on user delete (FK-safe)
- Validate cost create/update bodies with zod
- Unique index (tool_id, voter_token) + 409 on race duplicate ratings
- Clamp audit limit, escape ilike wildcards in search, O(N) analytics queries

Frontend:
- tools-browse reads and syncs URL query params (fixes home 'View all' links)
- Invalidate analytics/top-tools/categories/features caches after mutations
- Sync category combobox input when the value changes externally
- Hide Write a Review for anonymous users, drop unreachable rating guard

lib/db/src/schema/tool-costs.ts

@@ -11,6 +11,6 @@ export const toolCostsTable = pgTable("tool_costs", {
   currency: text("currency").default("EUR"),
   renewalDate: timestamp("renewal_date", { withTimezone: true }),
   notes: text("notes"),
-  createdBy: integer("created_by").references(() => usersTable.id),
+  createdBy: integer("created_by").references(() => usersTable.id, { onDelete: "set null" }),
   createdAt: timestamp("created_at", { withTimezone: true }).notNull().defaultNow(),
 });