feat: add stock material search section + npx skills add install

- SKILL.md: new 'Finding stock materials' section (on-demand, not mandatory)
  - 5 material sources: 爱给网, B站素材酷, Tenor, GIPHY, Klipy
  - Language-based priority (Chinese users → 爱给网 + B站素材酷)
  - Semantic search term expansion guidance
  - B站素材酷: bcut-resource-search userscript or direct API
  - Anti-bot fallback: browser-based tools
- README.md + README.zh.md: add 'npx skills add' install method
  - Compatible with open agent skills ecosystem (73+ frameworks)
  - git clone as fallback option
  - New 'Stock Material Search' section

SKILL.md

@@ -247,6 +247,45 @@ The user will likely ask follow-ups: "what about this section?", "add a transiti
 
 **Completion criteria:** user is satisfied with the plan or explicitly ends the session.
 
+## Finding stock materials (optional, on demand)
+
+When the user needs editing materials — stickers, GIFs, meme video clips, B-roll — the agent can help search or provide links for the user to search themselves. This section is **only triggered when the user asks for materials**; it is never a mandatory step.
+
+### Material sources
+
+| Source | URL | Content | Best for |
+|---|---|---|---|
+| 爱给网 | https://www.aigei.com/ | Chinese meme video clips (热梗, 4.2万+), free download | Chinese-language creators (B站/抖音) |
+| B站素材酷 | https://cool.bilibili.com/ | Bilibili platform-native assets (video, audio, BGM, templates, stickers) | B站 creators; large Chinese meme collection |
+| Tenor | https://tenor.com/ | GIFs + stickers, 30+ languages incl. Chinese, free API | Quick GIF/sticker search |
+| GIPHY | https://giphy.com/ | Largest GIF library, 30+ languages, sticker channel | English/multilingual GIF search |
+| Klipy | https://klipy.com/ | Localized GIF/sticker/clip API, supports Chinese | API-integrated search, localization |
+
+### Priority by language
+
+If the user communicates in Chinese, **recommend 爱给网 and B站素材酷 first** — they have the most Chinese-relevant meme and sticker content. For non-Chinese users, Tenor and GIPHY are good defaults.
+
+### Search strategy
+
+- **Expand search terms** based on semantic understanding of the user's request. If the user says "I want a clip of someone looking shocked", search terms might include: "惊讶 / 震惊 / 吃惊 / 哇 / wtf / shocked / surprised". Use the user's language as the base, expand with synonyms and internet slang.
+- The agent can either **search directly** (using web tools or API calls) or **suggest expanded search terms** for the user to search manually.
+- If the user only wants links, provide the source URLs above and let the user search themselves.
+
+### B站素材酷 special handling
+
+B站素材酷 (cool.bilibili.com) has no built-in search function. Two options:
+
+1. **Recommend the userscript**: [bcut-resource-search](https://git.nite07.com/nite/bcut-resource-search) — a Tampermonkey script that adds search to 素材酷, supporting video, sticker/image, music, sound effect, and template categories.
+2. **Search via API directly**: the agent can read the userscript's source code to discover the API endpoints and make requests directly (via HTTP tools or curl). Note: the site has CORS restrictions and UA-based access control, so direct API calls may require appropriate headers. If the agent's HTTP tools are blocked, fall back to suggesting the userscript to the user.
+
+### Anti-bot fallback
+
+Some material sites may block automated access (anti-bot, Cloudflare, CAPTCHA). If a web request or HTTP tool is blocked:
+
+1. Try with different headers (User-Agent, Accept-Language) if the tool allows.
+2. Fall back to a browser-based tool (e.g., Playwright, Puppeteer, or any browser automation the agent's runtime provides) to access the content.
+3. If browser tools are also blocked, inform the user and provide the direct URL for manual search.
+
 ## Long-running operations
 
 Before any operation expected to take >1 minute (first-time `uv sync`, transcription of long videos, large frame extraction):