Precedent attachment UI in the compose screen

Surface the new POST/GET/DELETE /api/cases/{n}/precedents endpoints
in the compose screen as two insertion points:

1. A new case-level card "פסיקה כללית לדיון" at the top of the
   main column, for precedents that support the discussion intro
   rather than a specific threshold_claim / issue.
2. An inline "פסיקה תומכת" section inside each SubsectionCard,
   below the ChairEditor.

Both insertion points render a `<PrecedentsSection>` which shows a
list of `<PrecedentCard>` (citation + blockquote + optional chair
note + 📄 chip if a PDF was archived) followed by a `<PrecedentAttacher>`
popover trigger.

The Attacher is a Popover with cross-case typeahead: typing 2+
characters into the citation field hits /api/precedents/search and
shows distinct library matches; picking one prefills quote + chair
note but leaves them editable so customizing the quote for this
case doesn't mutate the library. An optional PDF/DOCX/DOC file can
be attached — it uploads first via POST .../upload-pdf and the
returned document_id is passed into the precedent create call.

The parent compose page issues a single useCasePrecedents query
and partitions the result by section_id into a Map so each
SubsectionCard renders its own slice without re-fetching.

shadcn Popover installed as a new primitive. sonner toasts wired
for success/error in both attach and delete flows.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

web-ui/src/components/ui/popover.tsx

@@ -0,0 +1,89 @@
+"use client"
+
+import * as React from "react"
+import { Popover as PopoverPrimitive } from "radix-ui"
+
+import { cn } from "@/lib/utils"
+
+function Popover({
+  ...props
+}: React.ComponentProps<typeof PopoverPrimitive.Root>) {
+  return <PopoverPrimitive.Root data-slot="popover" {...props} />
+}
+
+function PopoverTrigger({
+  ...props
+}: React.ComponentProps<typeof PopoverPrimitive.Trigger>) {
+  return <PopoverPrimitive.Trigger data-slot="popover-trigger" {...props} />
+}
+
+function PopoverContent({
+  className,
+  align = "center",
+  sideOffset = 4,
+  ...props
+}: React.ComponentProps<typeof PopoverPrimitive.Content>) {
+  return (
+    <PopoverPrimitive.Portal>
+      <PopoverPrimitive.Content
+        data-slot="popover-content"
+        align={align}
+        sideOffset={sideOffset}
+        className={cn(
+          "z-50 flex w-72 origin-(--radix-popover-content-transform-origin) flex-col gap-2.5 rounded-lg bg-popover p-2.5 text-sm text-popover-foreground shadow-md ring-1 ring-foreground/10 outline-hidden duration-100 data-[side=bottom]:slide-in-from-top-2 data-[side=left]:slide-in-from-right-2 data-[side=right]:slide-in-from-left-2 data-[side=top]:slide-in-from-bottom-2 data-open:animate-in data-open:fade-in-0 data-open:zoom-in-95 data-closed:animate-out data-closed:fade-out-0 data-closed:zoom-out-95",
+          className
+        )}
+        {...props}
+      />
+    </PopoverPrimitive.Portal>
+  )
+}
+
+function PopoverAnchor({
+  ...props
+}: React.ComponentProps<typeof PopoverPrimitive.Anchor>) {
+  return <PopoverPrimitive.Anchor data-slot="popover-anchor" {...props} />
+}
+
+function PopoverHeader({ className, ...props }: React.ComponentProps<"div">) {
+  return (
+    <div
+      data-slot="popover-header"
+      className={cn("flex flex-col gap-0.5 text-sm", className)}
+      {...props}
+    />
+  )
+}
+
+function PopoverTitle({ className, ...props }: React.ComponentProps<"h2">) {
+  return (
+    <div
+      data-slot="popover-title"
+      className={cn("font-heading font-medium", className)}
+      {...props}
+    />
+  )
+}
+
+function PopoverDescription({
+  className,
+  ...props
+}: React.ComponentProps<"p">) {
+  return (
+    <p
+      data-slot="popover-description"
+      className={cn("text-muted-foreground", className)}
+      {...props}
+    />
+  )
+}
+
+export {
+  Popover,
+  PopoverAnchor,
+  PopoverContent,
+  PopoverDescription,
+  PopoverHeader,
+  PopoverTitle,
+  PopoverTrigger,
+}