feat(web): redesign Knowledge as an editable wiki

Replaces the read-only stats dashboard with a three-pane wiki: a
navigator tree (group by folder/type/tag/entity), a reader/editor with
bare-slug auto-linking and revision history + diff, and a context rail
for backlinks and related notes. Adds a Cleanup mode for the drift
tools (duplicates, tag manager, orphans, trash) and a Cmd+K quick-open.

Also:
- Adds a real landing view (hero count, KPI row, Nomos-share meter,
  recently-updated, busiest tags) in place of the old "Select a note"
  empty state, and extends the design pass across the tree/reader/rail
  (kind icons instead of repeated text badges, accent-bar selection,
  constrained prose measure).
- Guards every note-selection path behind a confirm when there's an
  unsaved edit in progress, so switching notes can no longer silently
  discard a draft.
- Extracts the markdown-rendering CSS duplicated across ChatThread,
  EntityDetailContent, and the new WikiReader into a shared
  .markdown-body class in app.css, with ChatThread keeping only its
  decorative deltas.

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

web/src/lib/components/knowledge/WikiQuickOpen.svelte

@@ -0,0 +1,119 @@
+<script lang="ts">
+  // Cmd/Ctrl+K quick-open over every note title — the fast path once you
+  // already know roughly what you're looking for, as opposed to WikiTree's
+  // browse-by-group path for when you don't. Built on the Dialog primitive
+  // + a plain filtered list rather than shadcn-svelte's `command` component:
+  // that component's interactive CLI installer couldn't be driven
+  // non-interactively in this environment (it prompts to resolve overlapping
+  // dependency files), and re-deriving the same arrow-key/Enter list nav by
+  // hand here is a small amount of code for something this self-contained.
+  import type { KnowledgeListItem } from '$lib/api'
+  import * as Dialog from '$lib/components/ui/dialog'
+  import { Input } from '$lib/components/ui/input'
+  import StatusBadge from '$lib/components/StatusBadge.svelte'
+  import { onDestroy } from 'svelte'
+
+  let {
+    open = $bindable(false),
+    items,
+    onSelect
+  }: {
+    open: boolean
+    items: KnowledgeListItem[]
+    onSelect: (slug: string) => void
+  } = $props()
+
+  let query = $state('')
+  let activeIndex = $state(0)
+  let inputEl = $state<HTMLInputElement | null>(null)
+
+  const results = $derived.by(() => {
+    const q = query.trim().toLowerCase()
+    const pool = q
+      ? items.filter(
+          (it) =>
+            it.title.toLowerCase().includes(q) ||
+            it.slug.toLowerCase().includes(q) ||
+            it.tags.some((t) => t.toLowerCase().includes(q))
+        )
+      : items
+    return pool.slice(0, 30) // 102 notes total — cap the render, not the match
+  })
+
+  $effect(() => {
+    void results // dependency only — re-run when the result set changes
+    activeIndex = 0
+  })
+
+  // Reset on every open so quick-open never remembers the last search, and
+  // focus the input once the dialog has actually mounted it.
+  $effect(() => {
+    if (open) {
+      query = ''
+      queueMicrotask(() => inputEl?.focus())
+    }
+  })
+
+  function choose(slug: string): void {
+    onSelect(slug)
+    open = false
+  }
+
+  function handleKeydown(e: KeyboardEvent): void {
+    if (!open) return
+    if (e.key === 'ArrowDown') {
+      e.preventDefault()
+      activeIndex = Math.min(activeIndex + 1, results.length - 1)
+    } else if (e.key === 'ArrowUp') {
+      e.preventDefault()
+      activeIndex = Math.max(activeIndex - 1, 0)
+    } else if (e.key === 'Enter') {
+      e.preventDefault()
+      const hit = results[activeIndex]
+      if (hit) choose(hit.slug)
+    }
+  }
+
+  // A window-level listener rather than one on Dialog.Content: bits-ui's
+  // Dialog renders its content through a portal with its own focus-trap
+  // wiring, and an onkeydown prop passed straight through to Content did not
+  // reliably receive ArrowDown/Enter in testing (focus landing inside the
+  // trap didn't guarantee the event reached the element this component
+  // attached the listener to). Capturing at the window and gating on `open`
+  // sidesteps that entirely — Escape-to-close is still bits-ui's own
+  // behavior, this only adds the list-navigation keys.
+  window.addEventListener('keydown', handleKeydown)
+  onDestroy(() => window.removeEventListener('keydown', handleKeydown))
+</script>
+
+<Dialog.Root bind:open>
+  <Dialog.Content
+    class="top-[20%] max-w-lg -translate-y-0 gap-0 p-0 sm:max-w-lg"
+    showCloseButton={false}
+  >
+    <Input
+      bind:ref={inputEl}
+      bind:value={query}
+      placeholder="Jump to a note…"
+      class="h-11 rounded-b-none border-0 border-b px-3 text-sm focus-visible:ring-0"
+    />
+    <div class="max-h-80 overflow-y-auto p-1">
+      {#each results as it, i (it.slug)}
+        <button
+          type="button"
+          class="flex w-full items-center gap-2 rounded px-2 py-1.5 text-left text-sm {i ===
+          activeIndex
+            ? 'bg-primary/10 text-primary'
+            : 'hover:bg-muted/50'}"
+          onclick={() => choose(it.slug)}
+          onmouseenter={() => (activeIndex = i)}
+        >
+          <span class="min-w-0 flex-1 truncate">{it.title}</span>
+          <StatusBadge kind="type" value={it.kind} class="shrink-0 text-[9px]" />
+        </button>
+      {:else}
+        <p class="py-6 text-center text-xs text-muted-foreground">No notes match "{query}".</p>
+      {/each}
+    </div>
+  </Dialog.Content>
+</Dialog.Root>