chore: replace the org PR template with a merge brief

[JuaniRios]

Replaces the org default PR template with a merge brief: live effect, risk, decisions, proof, and rollout, written for the person who approves the merge. Agents now review the code line by line, so the body stops explaining the code.

Live effect: new PRs opened on GitHub start from this template in every ST0x repo without its own template · Risk: low (no money path, no keys or IAM, docs only, easy to undo) · Ships: on merge · Blocks: ST0x-Technology/st0x.issuance#428, ST0x-Technology/st0x.liquidity#1576, ST0x-Technology/event-sorcery#60

Decisions

• One org template, not a copy per repo, so the format has one source. The three PRs above delete the repo copies that would override it. pull_request_template.md
• Drops the Checks list. CI shows the same things, and a ticked box proves nothing.

Risks

• gt submit only reads templates inside the repo, so PRs opened from the Graphite CLI start with an empty body. Most ST0x repos already work that way.

Proof

• Tried the format on a real infra PR. The body went from 456 words to about 160, and it gained the plan result and a rollback trap that the old body missed.
• Not verified: that GitHub loads the template on a new PR. That only shows after the merge.

🤖 Generated with Claude Code

[JuaniRios]

• chore: replace the org PR template with a merge brief #12 👈 (View in Graphite)
• main

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