One test proves cross-forge following end to end: parent commits, child checks, take pull opens, owner merges #2662

I added test/follow-e2e.test.ts, which runs the whole follow path in one test. It passes in under a second, and the type check and test/check-list.test.ts pass. I only ran those three, not the full check.

The test uses a parent bare repository cloned from the child's repo, so they share history. It follows the same pattern as test/spawn-take.test.ts: local paths only, no network, and checkUpstream called by hand with no timers.

1. The parent commits twice.
2. The first check gives behind 2 and files one tell-me card listing both commits.
3. setChainMode switches the child to take-updates. The next check opens one pull on forge/take-updates whose body lists both commits, and the default branch is unchanged.
4. mergePull merges that pull as the owner. The next check gives behind 0, says "up to date", and leaves no open take pull.
5. After a conflicting parent commit, the check opens one issue naming a.txt. A second check opens no pull and adds no second issue, and main stays where it was.

Gate: GATE in scripts/gate.ts no longer exists. The gate is now every test/*.test.ts minus EXCLUDED, so the new file is gated without an edit.

Production code: I found no seam between the pieces, so nothing under src/ changed.

Left out: the parent is a bare repository, not a second running forge app, so the test doesn't cover how a real parent's address is built from parent.json. It passes remote: to checkUpstream instead.

Closes #2659

I added test/follow-e2e.test.ts, which runs the whole follow path in one test. It passes in under a second, and the type check and test/check-list.test.ts pass. I only ran those three, not the full check.

The test uses a parent bare repository cloned from the child's repo, so they share history. It follows the same pattern as test/spawn-take.test.ts: local paths only, no network, and checkUpstream called by hand with no timers.

1. The parent commits twice.
2. The first check gives behind 2 and files one tell-me card listing both commits.
3. setChainMode switches the child to take-updates. The next check opens one pull on forge/take-updates whose body lists both commits, and the default branch is unchanged.
4. mergePull merges that pull as the owner. The next check gives behind 0, says "up to date", and leaves no open take pull.
5. After a conflicting parent commit, the check opens one issue naming a.txt. A second check opens no pull and adds no second issue, and main stays where it was.

Gate: GATE in scripts/gate.ts no longer exists. The gate is now every test/*.test.ts minus EXCLUDED, so the new file is gated without an edit.

Production code: I found no seam between the pieces, so nothing under src/ changed.

Left out: the parent is a bare repository, not a second running forge app, so the test doesn't cover how a real parent's address is built from parent.json. It passes remote: to checkUpstream instead.