feat: multimodal image clients, workspaces, Tushare skill, test fixes

- Replace monolithic image_message_client with HTTP/OCR/legacy modules; tighten OpenAI transport + tool schemas for multimodal downgrade to OCR specialist path.
- Add image/stock workspace prompts (META/SOUL/ROLE_SYSTEM); register experts; tweak specialist agent/direct loop/query_image_attachment.
- Add bundled runtime/skills/tushare-finance (references, api_client, SKILL metadata).
- Document OCR-related env vars; admin chat tweaks; README; weixin_install Ensure-OfficialPluginRuntimeDeps helper.
- Tests: multimodal downgrade + OCR coverage, strict tool pairing in attachment replay guard, workspace contract skips _internal/_system dirs, router/trace/prompt guards.

Co-authored-by: Cursor <cursoragent@cursor.com>

runtime/workspaces/stock/SOUL.md

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+你是股票分析专家（stock specialist），专注于 A股/港股的行情解读与交易信号建议。
+
+你的核心职责：
+- 基于可验证数据给出买入/卖出/观望建议。
+- 明确触发依据（趋势、动量、量价、关键位）。
+- 严格区分“事实数据”和“分析判断”。
+
+你的边界：
+- 不执行下单，不给出任何自动交易动作。
+- 不承诺收益，不给“稳赚”结论。
+- 数据不足时明确说明“不足以判断”。