feat(ui): Phase 2 — issue detail tab + dashboard widget

Plugin now mounts two React components inside Paperclip via the
SDK's UI slot mechanism. Both are read-only views over data the
plugin worker fetches from legal-ai on demand.

## Slots

* **LegalCaseTab** (type: detailTab, entityTypes: ["issue"])
  Mounted as a "ערר" tab on every issue page. Shows case summary
  (status / practice_area / appeal_subtype), legal_arguments
  grouped by party (עוררים/ועדה/משיבה/מבקשי היתר), attached
  precedents, and open missing_precedents.

* **LegalCasesWidget** (type: dashboardWidget)
  Dashboard tile with case counts by status + 7-day activity.

## Worker handlers (ctx.data.register)

Five handlers added at the end of setup() — all read-only over the
existing legal-ai HTTP API, all wrapped in try/catch so a transient
failure shows a placeholder instead of crashing the host:

- legal-case-summary           → /api/cases/{n}/details
- legal-case-arguments         → /api/cases/{n}/legal-arguments
- legal-case-precedents        → /api/cases/{n}/precedents
- legal-case-missing-precedents → /api/missing-precedents?case_number=&status=open
- legal-dashboard-stats        → in-memory aggregation over /api/cases

case_number is resolved from plugin state (scopeKind=issue,
stateKey=legal-case-number) — populated by legal_case_create.

## Build pipeline

- esbuild.ui.config.mjs uses createPluginBundlerPresets from the SDK
  to build src/ui/index.tsx → dist/ui/index.js (13.5kb, react +
  @paperclipai/plugin-sdk/ui externalized)
- package.json: build = "build:worker" (tsc) + "build:ui" (esbuild)
- tsconfig.json: jsx=react-jsx, lib += DOM
- New deps: react@19, @types/react, esbuild

## Manifest

- capabilities += ui.detailTab.register, ui.dashboardWidget.register
- entrypoints.ui = "dist/ui"
- ui.slots declared with entityTypes (not "entities" — fixed against
  PluginUiSlotDeclaration validator)

## Verified

- tsc + esbuild + biome clean
- Plugin re-installs (20 capabilities) and activates with worker
  + 8 tools + 3 jobs + 1 webhook + 2 event subs

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

esbuild.ui.config.mjs

@@ -0,0 +1,27 @@
+import { build } from "esbuild";
+import { createPluginBundlerPresets } from "@paperclipai/plugin-sdk/bundlers";
+import { fileURLToPath } from "node:url";
+import { dirname } from "node:path";
+
+const __dirname = dirname(fileURLToPath(import.meta.url));
+
+const presets = createPluginBundlerPresets({
+	pluginRoot: __dirname,
+	uiEntry: "src/ui/index.tsx",
+	outdir: "dist",
+	sourcemap: true,
+	minify: false,
+});
+
+if (!presets.esbuild.ui) {
+	throw new Error("UI preset missing — check createPluginBundlerPresets input");
+}
+
+await build({
+	...presets.esbuild.ui,
+	// Ensure JSX runtime is bundled-resolved at host runtime through React peer.
+	jsx: "automatic",
+	logLevel: "info",
+});
+
+console.log("[esbuild] UI bundle written to dist/ui/index.js");