feat: delete traffic targets and LLM task conversations from UI

Add delete controls to the Traffic and LLM Records pages so users can
purge recorded data without hand-editing the data volume.

Traffic page:
- Host target picker (Popover with checkboxes + select-all toggle)
- Exact-match batch delete for multiple hosts (DELETE /api/traffic/hosts)
- Substring delete for the host-filter input (DELETE /api/traffic?host=)
- Orphaned content-addressed blob garbage collection after deletes
- Distinct-hosts endpoint (GET /api/traffic/hosts) for the picker

LLM Records page:
- Task picker dropdown (distinct task_id + record counts)
- Per-task delete (DELETE /api/llm/records?task=)

Other:
- Add /dist/ to .gitignore (build artifact)
- Extend traffic_test.go with DeleteHost, DeleteHostsExact, Hosts tests
- Fix Popover render bug (replace ScrollArea that broke height calc)
- Remove fade/zoom animation on the host picker Popover

web/src/lib/mock/data.ts

@@ -8,7 +8,7 @@ import type {
   ConvTokenSummary, DailyTokenBucket, Edge, Finding, InterceptApprovalRow,
   InterceptPending, InterceptRule, LLMProfile, MCPServer, MCPTool, PromptVar,
   PromptVersion, Settings, SkillItem, Stats, TaskNode, Task, TokenTotal,
-  TokenUsage, Tool, TrafficResp, TrafficDetail,
+  TokenUsage, Tool, TrafficResp, TrafficDetail, TrafficHost, LLMTask,
 } from "@/lib/types";
 
 const T = (iso: string) => iso; // readability helper for timestamps
@@ -341,6 +341,11 @@ export const traffic: TrafficResp = {
   })),
 };
 
+// Distinct hosts with counts, derived from the exchanges above (target picker).
+const hostCounts: Record<string, number> = {};
+for (const [, host] of exchanges) hostCounts[host] = (hostCounts[host] ?? 0) + 1;
+export const trafficHosts: TrafficHost[] = Object.entries(hostCounts).map(([host, count]) => ({ host, count }));
+
 export const trafficDetail: TrafficDetail = {
   req: `GET /v1/orders?id=1002 HTTP/1.1
 Host: api.acme.com
@@ -641,6 +646,11 @@ export const llmRecords = [
   { id: 4, ts: T("2026-08-09T02:16:05Z"), model: "claude-opus-4-8", profile_name: "默认", session_id: "exp1-worker-i18", task_id: "t-001", worker: "worker-2", latency_ms: 900, input_tokens: 7600, output_tokens: 0, cache_read: 5200, cache_write: 0, status: "error", error: "429 Too Many Requests（已退避重试）" },
 ];
 
+// Distinct tasks with counts, derived from llmRecords above (task picker).
+const llmTaskCounts: Record<string, number> = {};
+for (const r of llmRecords) if (r.task_id) llmTaskCounts[r.task_id] = (llmTaskCounts[r.task_id] ?? 0) + 1;
+export const llmTasks: LLMTask[] = Object.entries(llmTaskCounts).map(([task_id, count]) => ({ task_id, count }));
+
 export function llmRecordDetail(id: number) {
   const item = llmRecords.find((r) => r.id === id) ?? llmRecords[0];
   return {

web/src/lib/mock/handler.ts

@@ -90,6 +90,9 @@ function route(m: string, path: string, seg: string[], q: URLSearchParams, b: Re
 
   // ── traffic / audit / settings ──
   if (path === "/audit") return D.audit;
+  if (path === "/traffic" && m === "DELETE") return { deleted: 0 };
+  if (path === "/traffic/hosts" && m === "DELETE") return { deleted: (b.hosts as unknown[])?.length ?? 0 };
+  if (path === "/traffic/hosts") return { hosts: D.trafficHosts };
   if (path === "/traffic") return D.traffic;
   if (path === "/traffic/exchange") return D.trafficDetail;
   if (path === "/settings" && m === "GET") return D.settings;
@@ -104,6 +107,8 @@ function route(m: string, path: string, seg: string[], q: URLSearchParams, b: Re
 
   // ── LLM ──
   if (path === "/llm/records" && m === "GET") return { records: D.llmRecords, total: D.llmRecords.length };
+  if (path === "/llm/records" && m === "DELETE") return { deleted: 0 };
+  if (path === "/llm/records/tasks") return { tasks: D.llmTasks };
   if (seg[0] === "llm" && seg[1] === "records" && seg.length === 3 && m === "GET") return D.llmRecordDetail(Number(seg[2]));
   if (path === "/llm" && m === "GET") return D.llmConfig;
   if (path === "/llm" && m === "POST") return { ok: true };