feat: add scheduler jobs and content filters

[bg6jxd]

Summary

• Add a multi-instance scheduler with isolated job configuration, browser profile, run history, logs, artifacts, and a scheduler WebUI.
• Add content filters for publish time and platform metrics, wired into search, detail, and creator flows before storage/comment/media work.
• Add scheduler artifact summaries with works list, comment word cloud, artifact actions, and docs for the new workflows.

Compatibility with latest main

• Rebased on latest origin/main before opening this PR.
• Kept upstream WebUI/build output changes intact; this PR adds scheduler_webui separately and does not remove existing webui assets.
• Resolved Zhihu creator-flow changes by preserving the current url_token callback API and applying filters inside the callback.

Responsible-use notes

• Does not increase default crawl scale.
• Filters only reduce saved/comment/media targets.
• Scheduler keeps one active run per job and preserves the project non-commercial learning-use boundary.

Tests

• UV_CACHE_DIR=/private/tmp/mediacrawler-uv-cache uv run pytest tests
• node --check scheduler_webui/app.js
• git diff --check origin/main...HEAD