fix(users): drop dead user_reputations JOIN that broke Members page + audit

Root cause: gateway migration 0016 removed the per-user reputation feature
(DROP TABLE user_reputations), but the backend still LEFT JOINed
pgUserReputationsTable in dashboard listUsers/getUserDetail and the chatbot
get_user_reputation tool. Against the live DB these queries raised 42P01
(undefined_table) -> the new /users page could never load (oRPC WS error).

Fix:
- dashboard.repository.ts: remove reputation columns/join from listUsers and
  getUserDetail (data sourced only from messages + user_profiles).
- chatbot.tools.ts: get_user_reputation now returns honest 'unavailable'
  (feature removed) instead of querying the dropped table.
- chatbot.toolDefs.ts: update tool description so the LLM doesn't advertise
  a dead feature.
- frontend types/users view: drop trust_score/clean_message_streak/
  total_infractions/last_infraction_at; derive risk label from real flagged%
  and add warn_count to the inspector (real available data).

Verified: backend+frontend tsc clean, biome clean, 37 unit tests pass,
query tested against live DB (returns real members), build green.

services/frontend/src/lib/types/dashboard.ts

@@ -57,16 +57,10 @@ export interface DashboardUser {
   clean_count?: number;
   warn_count?: number;
   last_message_at?: number | null;
-  trust_score?: number | null;
-  clean_message_streak?: number | null;
-  total_infractions?: number | null;
-  last_infraction_at?: number | null;
 }
 
 export interface DashboardUserDetail extends DashboardUser {
   last_analyzed_at?: number | null;
-  clean_message_streak: number | null;
-  total_infractions: number | null;
   clean_count: number;
   warn_count?: number;
   recent_messages: MessageRecord[];