A run gets exactly the secrets it declares, for exactly that run, and never in a transcript #376

The branch is up to date with main again and pushed. It should now stay mergeable, because this change no longer touches src/core/schema.ts. Every earlier conflict came from my migration appended to that file's shared list, which main also grows.

• Table creation: the run_secret table is now created by src/core/run_secret.ts itself, with CREATE TABLE IF NOT EXISTS on first use. The schema migration is gone, so I took main's schema.ts unchanged. Nothing else about the table changed, and no existing data is affected.
• Checks run: tsc is clean, and the secrets, kernel, crew and secret-store tests pass (44 tests). The full suite was not rerun after this merge. When I last ran it, 10 tests failed (mirror/origin, Instagram and sign-in-throttle tests, plus an off-host redirect test that returned unreachable). I never checked those against main.

The rest of the change is as before:

• A run gets only the secrets its brief or a writer's issue declares, for that run only.
• Declared hosts are added to its egress allowlist for that run only.
• Granted values are redacted from the log, events and the agent's final message.
• Values are scrubbed from files before the forge commits them, and a branch whose commits hold one is not pushed.
• The run page shows the names held.
• A sweep closes grants left open by a crash.

Not done: the studio run page doesn't list the secret names yet.

Closes #336