feat(code): add commit and pr attribution to system prompt

[adboio]

Problem

we explicitly instruct the (cloud) agent to not include any attribution lines -- presumably to avoid the default claude code stuff

however, this means there's also no attribution back to posthog code

Changes

• cloud: replaces the "no attribution" prompting with instructions to add commit trailers (see feat(code): add commit trailers for attribution #1431 ) and PR body footers
• local: adds new commit+PR attribution instructions, which hopefully will override whatever is injected by claude code

How did you test this?

i haven't yet 🙈

[adboio]

Warning

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• feat(code): persist PR URLs to backend & emit file activity events #1434
• feat(code): add attribution to PR body from UI #1433
• feat(code): add commit and pr attribution to system prompt #1432 👈 (View in Graphite)
• feat(code): add commit trailers for attribution #1431
• Add staged file tracking and selective commit support #1429
• Fix git diff to compare against HEAD instead of working directory #1422
• main

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