Deploy: main into prod (#343)

Brings `prod`, which upaas deploys, up to `main` at `9cf9cdd`, the merge of #321. `prod` was cut from `main` at `251cb3d` (1.0.0b1).

What it deploys is everything listed in #321. For running it:

- With `WEBHOOKER_ENVIRONMENT` unset, the instance runs as `prod` and sends no `Access-Control-Allow-Origin: *`.
- Each event database gains its new indexes the first time it is opened after the upgrade.
- `webhooker_delivery_retries_total` no longer counts a circuit breaker holding back a delivery that is already `retrying`.

Not in this PR yet: #340, in which the container sets its own data directory owner and mode before start. It is in progress on `next`. Once it reaches `main`, this PR carries it, because the PR follows `main`.

Model: opus-5-5
Co-authored-by: Jeffrey Paul <1+sneak@noreply.example.org>
Reviewed-on: #343
Co-authored-by: clawbot <35+clawbot@noreply.example.org>

internal/delivery/circuit_breaker_test.go

@@ -267,7 +267,7 @@ func TestCircuitBreaker_CooldownRemaining_ClosedReturnsZero(
 	)
 }
 
-func TestCircuitBreaker_CooldownRemaining_HalfOpenReturnsZero(
+func TestCircuitBreaker_CooldownRemaining_HalfOpenReturnsCooldown(
 	t *testing.T,
 ) {
 	t.Parallel()
@@ -282,9 +282,11 @@ func TestCircuitBreaker_CooldownRemaining_HalfOpenReturnsZero(
 
 	require.True(t, cb.Allow())
 
-	assert.Equal(t, time.Duration(0),
+	// The cooldown newShortCooldownCB gives the breaker.
+	assert.Equal(t, 50*time.Millisecond,
 		cb.CooldownRemaining(),
-		"half-open circuit should have zero cooldown remaining",
+		"a delivery refused while half-open should wait "+
+			"a whole cooldown",
 	)
 }