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

templates/target_edit.html

@@ -69,7 +69,7 @@
             <div class="form-group">
                 <label for="max_retries" class="label">Max retries</label>
                 <input type="number" id="max_retries" name="max_retries" value="{{.Target.MaxRetries}}" min="0" max="20" class="input">
-                <p class="text-xs text-gray-500 mt-1">0 is fire-and-forget: one attempt, no circuit breaker.</p>
+                <p class="text-xs text-gray-500 mt-1">This is the total number of delivery attempts, not retries on top of the first: a value of 3 makes three attempts in all. 0 means a single attempt with no retries and no circuit breaker.</p>
             </div>
             {{end}}