feat(timezone): make all user/LLM-facing timestamps timezone-configurable (#129)

Add top-level `timezone` config option (default: "system") supporting
IANA names and UTC offset strings (ECMA-402 2024).

- Introduce unified `src/utils/time.ts` module with formatForLLM,
  formatLocalDate, formatLocalDateTime, startOfLocalDay, nowInstantISO
- Converge 4 scattered time helpers into the single module
- L1 extraction / auto-recall / scene-extraction / persona-generation
  prompts now emit ISO 8601 with explicit UTC offset
- Add timezone declaration to LLM system prompts
- Local-day shard boundaries and cleaner cutoff follow configured tz
- Storage instants (SQLite/TCVDB) remain UTC — no data migration needed
- 38 unit tests covering IANA, offset, DST, half-hour zones, fallback

index.ts

@@ -23,6 +23,7 @@ import { createRequire } from "node:module";
 import type { OpenClawPluginApi } from "openclaw/plugin-sdk/core";
 import { parseConfig } from "./src/config.js";
 import type { MemoryTdaiConfig } from "./src/config.js";
+import { initTimeModule, getActiveTimeZone } from "./src/utils/time.js";
 import { registerOffload } from "./src/offload/index.js";
 import {
   setPreferredEmbeddedAgentRuntime,
@@ -190,6 +191,9 @@ export default function register(api: OpenClawPluginApi) {
     throw err;
   }
 
+  // Initialize unified time module (must happen before any timestamp formatting)
+  initTimeModule({ timezone: cfg.timezone }, api.logger);
+
   // ============================
   // Hook policy auto-patch (v2026.4.24+ compat)
   // ============================