docs(FN-823): clarify agent log content is never truncated per-entry

- Clarify in dashboard README that agent log entries are never truncated
- Add maxLength safeguards in store (getAgentLog), routes, useAgentLogs, and useMultiAgentLogs hooks
- Add tests for store, AgentLogViewer component, useAgentLogs hook, useMultiAgentLogs hook, and dashboard routes
- All tests verify that log text and detail fields are preserved in full without per-entry truncation

packages/dashboard/app/hooks/useMultiAgentLogs.ts

@@ -4,6 +4,14 @@ import { fetchAgentLogs } from "../api";
 
 export const MAX_LOG_ENTRIES = 500;
 
+/**
+ * Cap the total number of log entries to `MAX_LOG_ENTRIES`.
+ *
+ * This is a **whole-list cap** — it limits how many entries are kept
+ * in memory, not the content of any individual entry.  Per-entry `text`
+ * and `detail` fields are never truncated anywhere in the pipeline
+ * (persistence → API → SSE → hook → rendering).
+ */
 function capLogEntries(entries: AgentLogEntry[]): AgentLogEntry[] {
   return entries.length > MAX_LOG_ENTRIES
     ? entries.slice(-MAX_LOG_ENTRIES)