feat(ui): 15-point UX overhaul — affordances, feedback, and navigation

Address friction points identified in a full interface audit:
- Re-add status badge to dashboard tiles so run state is visible at a glance
- Add active nav indicator and SSE connection health monitor (live/stale)
- Show manual registration form by default instead of hiding behind <details>
- Add copy-to-clipboard buttons on SSH hold command and quick-register one-liner
- Replace tooltip-only profile descriptions with inline visible text
- Clarify non-destructive toggle with explicit stage impact description
- Replace disabled "Start vetting" button with actionable offline guidance
- Swap browser confirm() dialogs for styled inline confirmations
- Add colored badge to spec diffs summary visible when collapsed
- Add distinct "cancelled" mood for cancelled runs (vs idle)
- Add match count to log search and aria-label for accessibility
- Add styled 404 page rendered inside the app shell

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/web/templates/active_step.templ

@@ -39,7 +39,8 @@ templ ActiveStep(d ActiveStepData) {
 				</ol>
 			}
 			<div class="log-search-wrap">
-				<input class="log-search" type="search" placeholder="Search this step" data-step={ d.Stage.Name }/>
+				<input class="log-search" type="search" placeholder="Search this step" data-step={ d.Stage.Name } aria-label={ "Search " + d.Stage.Name + " logs" }/>
+				<span class="log-match-count"></span>
 			</div>
 			<div
 				class="log-pane"