Capture member/filter/spam events for the dashboard (Phase 6b)

Light up the moderation dashboard's previously-empty widgets by persisting the
event streams the bot only reacted to in-memory before.

Schema (bot-owned)
- member_events: join/leave, with invite_code/inviter_* for best-effort invite
  attribution on joins
- filter_hits: word / foreign-invite filter deletions (matched + action_taken)
- spam_hits: rate_limit / mass_mention / mass_emoji detections

Bot
- new models memberEvents/filterHits/spamHits
- guildMemberAdd records the join with invite attribution; new inviteTracker.js
  keeps an invite-use cache (GuildInvites intent + inviteCreate/inviteDelete) and
  diffs it on join to find which invite was used — best-effort, never blocks
  auto-role
- new guildMemberRemove records leaves
- messageFilter records filter/spam hits alongside the existing warn/mute;
  inviteFilter now returns the offending code; detectSpam identifies which spam
  rule tripped (preserving the rate-limit-first side-effect order)
- mod_actions still logs the resulting warn/mute — the new tables are additive

Server
- summary extended with joins/leaves/invite_joins/filter_hits/spam_hits per window
- new feeds: /api/v1/admin/moderation/{members,filter-hits,spam-hits}

Client
- overview now shows 8 tiles (mod actions + joins/leaves/filter/spam, joins tile
  notes "N via invite") plus an Events panel with Members/Filter/Spam tabs;
  removed the coming-soon note

Verified: 119 server unit tests, client build, 14-check DB-backed smoke, and a
browser click-through of every tile and events tab (incl. invite attribution).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019rao86n5cXpwAyjdBFEshV

server/swagger/swagger-output.json

@@ -3940,6 +3940,90 @@
         ]
       }
     },
+    "/api/v1/admin/moderation/members": {
+      "get": {
+        "tags": [
+          "Admin · Moderation"
+        ],
+        "summary": "Recent member join/leave events (optionally filtered by type)",
+        "description": "",
+        "parameters": [
+          {
+            "name": "type",
+            "in": "query",
+            "schema": {
+              "type": "string"
+            }
+          }
+        ],
+        "responses": {
+          "200": {
+            "description": "OK"
+          },
+          "500": {
+            "description": "Internal Server Error"
+          }
+        },
+        "security": [
+          {
+            "cookieAuth": []
+          },
+          {
+            "bearerAuth": []
+          }
+        ]
+      }
+    },
+    "/api/v1/admin/moderation/filter-hits": {
+      "get": {
+        "tags": [
+          "Admin · Moderation"
+        ],
+        "summary": "Recent automated content-filter hits",
+        "description": "",
+        "responses": {
+          "200": {
+            "description": "OK"
+          },
+          "500": {
+            "description": "Internal Server Error"
+          }
+        },
+        "security": [
+          {
+            "cookieAuth": []
+          },
+          {
+            "bearerAuth": []
+          }
+        ]
+      }
+    },
+    "/api/v1/admin/moderation/spam-hits": {
+      "get": {
+        "tags": [
+          "Admin · Moderation"
+        ],
+        "summary": "Recent automated spam-detection hits",
+        "description": "",
+        "responses": {
+          "200": {
+            "description": "OK"
+          },
+          "500": {
+            "description": "Internal Server Error"
+          }
+        },
+        "security": [
+          {
+            "cookieAuth": []
+          },
+          {
+            "bearerAuth": []
+          }
+        ]
+      }
+    },
     "/api/v1/admin/moderation/user/{discordId}": {
       "get": {
         "tags": [