Say max_retries is the total attempt count, not a retry count (closes #316)

The help text under the field on both target forms and the max_retries rows in the README now say the number is the total number of delivery attempts: 0 is a single attempt with no retries and no circuit breaker, and N is N attempts in total. The delivery code already worked this way; only the wording was wrong, so an operator wanting one try plus two retries would have entered 2 instead of 3. A UI copy test renders both forms and pins the wording. Delivery behaviour is unchanged.

Model: opus-4-8 (implementation); fable-5-1 (merge)

README.md

@@ -1507,7 +1507,7 @@ events should be forwarded.
 | `type`           | TargetType | One of: `http`, `slack`, `database`, `log` |
 | `active`         | boolean    | Whether deliveries are enabled (default: true) |
 | `config`         | JSON text  | Type-specific configuration |
-| `max_retries`    | integer    | Maximum retry attempts for `http` and `slack` targets (0 = fire-and-forget, >0 = retries with backoff and a circuit breaker). Ignored by `database` and `log` targets |
+| `max_retries`    | integer    | Total delivery attempts for `http` and `slack` targets, not retries on top of the first: 0 is a single fire-and-forget attempt with no retries and no circuit breaker, and a value of N makes N attempts in all, with exponential backoff and a per-target circuit breaker. Ignored by `database` and `log` targets |
 | `max_queue_size` | integer    | Stored and shown on the target's detail view, but not enforced anywhere yet: nothing in the delivery engine consults it. Queue depth is set by the two fixed 10,000-entry channels |
 
 **Relations:** Belongs to Webhook. Has many Deliveries.
@@ -1515,12 +1515,12 @@ events should be forwarded.
 **Target types:**
 
 - **`http`** — Forward the event as an HTTP POST to a configured URL.
-  Behavior depends on `max_retries`: when `max_retries` is 0 (the
-  default), the target operates in fire-and-forget mode — a single
-  attempt with no retries and no circuit breaker. When `max_retries` is
-  greater than 0, failed deliveries are retried with exponential backoff
-  up to `max_retries` attempts, protected by a per-target circuit
-  breaker.
+  `max_retries` is the total number of delivery attempts, not retries on
+  top of the first: when `max_retries` is 0 (the default), the target
+  operates in fire-and-forget mode, a single attempt with no retries and
+  no circuit breaker; a value of N makes up to N attempts in all,
+  retrying failed deliveries with exponential backoff and protecting them
+  with a per-target circuit breaker.
 - **`slack`** — Post the event as a formatted message to a
   Slack-compatible incoming webhook URL (`webhookUrl` in `config`). It
   is built on the same HTTP core as `http` and honours `max_retries`