Add campaign pageview tracking and /github redirect

[suguanYang]

Summary

• Add marketing_page_views first-party tracking so repeat campaign visits (including UTM 404 paths like /reddit?utm_source=reddit) are counted even when a first-touch cookie already exists.
• Expand acquisition capture to /github and any public path with UTM/oppref query params; provider captures session first, then pageview with the returned session id.
• Ship a client /github redirect page to https://github.com/Ontos-AI/knowhere so GA and first-party tracking can fire before leave, and point the landing header GitHub link at /github.

Test plan

• Visit /github and confirm brief redirect page, GA pageview, and a marketing_page_views row for /github
• Visit /reddit?utm_source=reddit and confirm 404 UI plus session + pageview rows
• Revisit a campaign URL with an existing kh_acquisition_session cookie and confirm pageviews still increment without overwriting first-touch session
• Confirm /, /claw, /comparison/*, /versus/* still capture first-touch as before
• Run pnpm db:migrate (or apply 0009_mushy_ezekiel) and acquisition attribution unit tests

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