feat: master-detail entity sheet, freshness in Entities table, live logo

Problem: the web UI felt dead and hard to navigate — the Entities table
had no health/freshness signal (just a meaningless row-mutation
timestamp), no way to see what was actually monitoring an entity,
sessions couldn't be reopened, and every drill-down was a full page
navigation that lost the list.

Change:
- Entities table: Updated column replaced with a health dot + relative
  "checked Xm ago", sourced from the backend's new health/last_check_at
  fields.
- New EntityDetailContent.svelte extracted from EntityDetail.svelte and
  shared between the full #/entity/:slug page and a new EntitySheet.svelte
  opened from the Entities table (master-detail, row click opens a panel
  instead of navigating away). Adds a Monitoring card listing the
  entity's check_defs (kind, interval, enabled/disabled with
  click-to-toggle via the existing PatchCheck endpoint) and renders
  attributes as key/value pairs instead of raw JSON.
- Sessions: fixed a bug where clicking a session loaded it into the
  chat store but never navigated to the chat page, so nothing appeared
  to happen. Added a SessionRail inside Chat so switching sessions
  never leaves the chat surface.
- Fixed the local dev proxy (vite.config.ts): production Caddy strips
  the /agent prefix before forwarding to nomos; the dev proxy didn't,
  so every session/chat fetch 404'd locally while working in prod.
- Found and fixed a real latent bug while testing the session fix:
  chat.ts's loadSessionMessages passed the persisted tool_calls array
  straight through, but nomos stores the tool_use and tool_result as
  two entries sharing one id. Chat.svelte's keyed {#each tool (tool.id)}
  throws on the duplicate key, which silently blanked the entire
  message list — invisible until sessions were actually clickable.
  Fixed by merging tool_calls by id before rendering, matching the
  shape the live-streaming path already produces.
- UI polish: sidebar logo is now just the omicron mark in white (was
  icon+text in the accent color); removed the sheet overlay's
  backdrop-blur (distracting per feedback); the Attributes/Relations/
  Signals grids used viewport-based lg:/3xl: breakpoints, which forced
  multi-column layouts based on browser width regardless of the sheet's
  actual rendered width — switched to Tailwind v4 container queries
  (@lg:/@2xl:/@3xl:) so layout responds to the real available width in
  both the full page and the narrower sheet.

Risk: reversible_low (UI-only; no destructive operations; the tool_calls
merge and dev-proxy fix are corrections to broken paths, not behavior
changes to working ones).

Verification: npx tsc --noEmit clean (excluding pre-existing unrelated
.svelte type-resolution warnings). Manually verified in the browser
preview against the live dev API: Entities table health column renders
correctly; clicking a row opens the EntitySheet with a populated
Monitoring card (16 checks for host:hubris, verified via psql that
check_defs.target_id links them correctly); clicking a session now
loads its full transcript inline (was blank before the tool_calls fix);
sheet has no blur and lays out single/multi-column correctly at the
sheet's actual width.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

web/src/pages/Chat.svelte

@@ -1,6 +1,7 @@
 <script lang="ts">
   import { messages, streaming, sendMessage, cancelStream, error } from '$lib/stores/chat'
   import ContextRail from '$lib/components/ContextRail.svelte'
+  import SessionRail from '$lib/components/SessionRail.svelte'
   import { Button } from '$lib/components/ui/button'
   import { Textarea } from '$lib/components/ui/textarea'
   import ArrowUpIcon from '@lucide/svelte/icons/arrow-up'
@@ -62,6 +63,11 @@
 </script>
 
 <div class="flex h-full min-h-0">
+  {#if showRail}
+    <div class="hidden md:block">
+      <SessionRail />
+    </div>
+  {/if}
   <div class="flex min-w-0 flex-1 flex-col">
     <div class="min-h-0 flex-1 overflow-y-auto">
       <div class="mx-auto flex max-w-3xl flex-col gap-5 p-4">