Make every clickable control look clickable, in two shared styles (closes #375)

Buttons keep btn-primary, btn-secondary and btn-danger and gain a
pointer cursor; the navigation links become btn-secondary buttons.
Every control that was plain coloured text (Copy, both Add, the row
actions, Resubmit, Replay, the back, footer and download links) now
uses btn-small, bordered at rest with hover and focus states. Both
styles are in static/css/style.css, which the layout now loads.

The event log's clickable rows become buttons, so they work by
keyboard; Replay moves beside its delivery's row. Rows on the webhook
page and in the event log wrap at phone width. The browser test now
checks that Copy reads "Copied".

Model: opus-5-5

README.md

@@ -1313,15 +1313,16 @@ A browser test in `internal/server` loads the webhook page and the event log
 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; an event 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 image build lint it but do not run it, and `make test` leaves it out
-(its file is built only with the `browser` build tag). Run it with
-`make test-browser` after changing `templates/` or `static/js/`: that builds
-`Dockerfile.browser`, which runs the test in a digest-pinned headless browser
-image, so the host needs no browser.
+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
+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
+image build lint it but do not run it, and `make test` leaves it out (its file
+is built only with the `browser` build tag). Run it with `make test-browser`
+after changing `templates/` or `static/js/`: that builds `Dockerfile.browser`,
+which runs the test in a digest-pinned headless browser image, so the host
+needs no browser.
 
 The package's tarball is committed as `3p/alpinejs-csp-3.14.9.tgz`, byte for
 byte as the npm registry publishes it. It is a dependency, not this repo's build
@@ -3007,7 +3008,7 @@ webhooker/
 │   ├── static.go              # //go:embed directive
 │   ├── css/input.css          # Tailwind input, source for tailwind.css (make css)
 │   ├── css/tailwind.css       # Generated stylesheet the pages load
-│   ├── css/style.css          # Older hand-written stylesheet, no longer loaded
+│   ├── css/style.css          # Hand-written: the shared button styles, loaded after tailwind.css
 │   ├── js/app.js              # Copy-to-clipboard, and the Alpine.js components
 │   └── js/alpine.min.js       # Alpine.js CSP build, extracted from 3p/ by make assets, not committed
 ├── templates/                 # Go HTML templates (base, login, sources, etc.)