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>

package.json

@@ -7,7 +7,9 @@
     "manifest": "dist/manifest.js"
   },
   "scripts": {
-    "build": "tsc",
+    "build": "tsc && node esbuild.ui.config.mjs",
+    "build:worker": "tsc",
+    "build:ui": "node esbuild.ui.config.mjs",
     "dev": "paperclip-plugin-dev-server",
     "format": "biome format --write src/",
     "format:check": "biome format src/",
@@ -15,11 +17,14 @@
     "biome:fix": "biome check --write src/"
   },
   "dependencies": {
-    "@paperclipai/plugin-sdk": "^2026.525.0"
+    "@paperclipai/plugin-sdk": "^2026.525.0",
+    "react": "^19.0.0"
   },
   "devDependencies": {
     "@biomejs/biome": "2.4.11",
     "@types/node": "^25.5.0",
+    "@types/react": "^19.0.0",
+    "esbuild": "^0.28.0",
     "typescript": "^6.0.2"
   }
 }