docs: improve p2p collection guide - teach model to obtain chat_id and tokens dynamically

feat: add private chat (p2p) message collection via user_access_token

fix: replace broken /search/v1/user with department traversal + batch_get_id

docs: add WeChat to data sources, clarify recommended export tools

docs: remove instability wording from chat export tools section

docs: add recommended WeChat chat export tools section

docs: sync README_EN.md with Chinese version

docs: move ex-skill promo above data sources table

docs: add cross-promotion for ex-skill in README

feat: add Slack auto collector

revert: remove image, restore original text layout

fix: rename image to bypass CDN cache

fix: brighter image and remove table border

feat: side-by-side layout for parallel sentences and Wandering Earth 2 image

feat: add Wandering Earth 2 image with side-by-side layout