Prompt History und Verbrauchsauswertung (#660), englische Hauptsprache (#661)

Prompt history: every run records its transcript (task, each model step with
tokens and cost, tool calls and results, engine follow-ups) - bounded in size,
scrubbed of recognisable secrets, system prompts stored once per text.
Retention in days per instance (default 14) and per agent (0 = never, -1 =
forever); an hourly janitor deletes what is past it, "never" also purges.

Usage analysis over run receipts: filter by period, agent, model, event, status,
cost and free text; sort by every column; totals over the whole filter; hourly
or daily series grouped by agent, model or event; markers for budget denials and
model changes; run detail with receipt, transcript, tool calls and approvals.

WebUI: Analysis > Token usage > Runs / Timeline, run detail, Prompt History with
retention settings. New code, comments and texts in English; texts come from
language packs (i18n/en.json, de.json) via modules/i18n.js. CLAUDE.md records
English as the main language.

Version 0.1.12.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/ClawdDotNet.Core/Config/AgentConfig.cs

@@ -145,6 +145,12 @@ public sealed class AgentConfig
     [JsonPropertyName("budget")]
     public AgentBudget Budget { get; set; } = new();
 
+    /// <summary>
+    /// #660: Per-agent retention of the prompt history. <c>null</c> retention = instance default.
+    /// </summary>
+    [JsonPropertyName("promptHistory")]
+    public Transcripts.AgentPromptHistorySettings PromptHistory { get; set; } = new();
+
     /// <summary>
     /// Übersetzt <see cref="ReasoningEffort"/> in das Anfragefeld. Null heißt:
     /// nichts mitschicken, das Modell denkt wie voreingestellt.