The forge computes the "unproposed work" flow alarm: a crew fork's branch has sat 6 h with no open pull #6391

Part of #5930 (the owner's fifth alarm, second half): an agent tree has commits not proposed as a pull for 6 h or more.

Done:

• [ ] src/flow/alarm_unproposed.ts, shaped like the other alarm_*.ts files: it fires when a branch in a crew member's fork of a repository has a head that is not on main, is not the head of any open pull, and is 6 h old or more.
• [ ] says names the oldest three branches with their owner and age.
• [ ] A test with a seeded fork: a 7 h branch with no pull fires; a branch that heads an open pull, or one merged into main, does not.

Files: src/flow/alarm_unproposed.ts, a test.

Risk: read branches through the git helpers the branches page uses; never shell out with branch names.

Before pushing: bun x tsc --noEmit and the tests you add or touch. Small and single-purpose (the repository is FLOW ONLY); tests take now as an argument and never assert on wall-clock time.