Give each event its own page and show bodies the same everywhere (closes #369)

Each row of the recent events on the webhook page links to the
event's own page, /hook/{id}/events/{eventID}, and expands to show its
body; only the newest starts expanded. The event's page shows its
details, its whole body and every delivery with its attempts.

One renderer, newBodyView with templates/event_body.html, shows a body
in all three places: whole up to 32 KiB, cut there in the lists with a
link to the event's page, JSON pretty-printed, a body of more than 200
lines or 32 KiB in a scrolling box, and a body that is not text left
out beside its download link. A resubmitted copy links to its
original's page.

Model: opus-5-5

README.md

@@ -1327,7 +1327,9 @@ under the real policy and checks that: both add forms stay hidden until Add is
 clicked; choosing Slack in the add target form leaves the HTTP fields out of
 what it submits, also after leaving the page and going back to it, when the
 browser restores the choice; the Copy button beside an entrypoint URL reads
-"Copied" once clicked; an event expands and collapses, and so do a delivery's
+"Copied" once clicked; of the recent events on the webhook page only the newest
+starts expanded, each expands and collapses, and Open leads to the event's own
+page; an event in the event log expands and collapses, and so do a delivery's
 attempts inside it; and at phone width the menu button opens and closes the
 mobile menu. It also fails if the browser reports a console warning or error,
 an uncaught exception, or anything the policy refused. `make check` and the
@@ -2889,7 +2891,8 @@ returns to the page that was asked for.
 | `POST` | `/hook/{id}/edit`        | Edit webhook submission |
 | `POST` | `/hook/{id}/delete`      | Delete webhook |
 | `GET`  | `/hook/{id}/events`      | Full Event Log |
-| `GET`  | `/hook/{id}/events/{eventID}/body` | Download an event's full stored body. The log page renders each body only up to its cap, so this is the only route that serves a whole one; it is offered wherever a body is shown truncated |
+| `GET`  | `/hook/{id}/events/{eventID}` | One event's own page: its details, its whole body and every delivery of it |
+| `GET`  | `/hook/{id}/events/{eventID}/body` | Download an event's stored body. The pages show a body as text, cut at 32 KiB in the recent events and the event log, and leave a binary one out, so this is the only route that serves the stored bytes; it is offered wherever a body is cut or binary |
 | `POST` | `/hook/{id}/deliveries/{deliveryID}/replay` | Replay a finished delivery: creates a new delivery for the same event against the target's current configuration (30 per minute per bucket, then `429`) |
 | `POST` | `/hook/{id}/events/{eventID}/resubmit` | Resubmit a stored event: creates a new event copying it and fans that out to every currently active target (30 per minute per bucket, then `429`) |
 | `POST` | `/hook/{id}/entrypoints` | Add entrypoint to webhook |