feat(opencode): native opencode addon — bottom-row project indicator + in-TUI switcher

Adds an opencode integration mirroring the existing pi and prime-agent addons.

The addon is a TUI plugin (`src/opencode-ext/open-mcpctl.tsx`) that:
- renders the active mcpctl project into opencode's `app_bottom` slot — the
  status row that also carries the token counter / model info,
- registers a `mcpctl.switch_project` command bound to `<leader>m` that opens a
  searchable `DialogSelect` project picker,
- switches live by re-pointing opencode's `mcpctl` MCP server at the new
  project's mcplocal endpoint via the SDK client (native MCP, no JSON-RPC code),
- persists state in `~/.mcpctl/opencode-state.json` (+ `.mcpctl-project` marker).

Pure helpers (`filterProjects`, `toolChangeAnnouncement`) live in
`projects.ts` so they are unit-tested.

`mcpctl config opencode --project X` provisions it: writes the plugin into
`~/.config/opencode/plugin/`, registers the `.tsx` in opencode.json's plugin
array (auto-discovery only matches {ts,js}), best-effort installs the TUI peer
deps (`@opentui/*`), and syncs skills into `~/.config/opencode/skill`.
`mcpctl skills sync --agent opencode` is added as a fourth shared-tree target.

Closes typecheck gap with `typecheck:opencode-ext` against the real
`@opencode-ai/plugin` + `@opentui/solid` types.

Tests: embed freshness, opencode-settings, projects helpers, skills agent
root. Full `pnpm run typecheck` + cli tests pass; completions regenerated.

package.json

@@ -16,7 +16,7 @@
     "clean": "pnpm -r run clean && rimraf node_modules",
     "db:up": "docker compose -f deploy/docker-compose.yml up -d",
     "db:down": "docker compose -f deploy/docker-compose.yml down",
-    "typecheck": "tsc --build && pnpm run typecheck:pi-ext",
+    "typecheck": "tsc --build && pnpm run typecheck:pi-ext && pnpm run typecheck:opencode-ext",
     "completions:generate": "tsx scripts/generate-completions.ts --write",
     "completions:check": "tsx scripts/generate-completions.ts --check",
     "rpm:build": "bash scripts/build-rpm.sh",
@@ -34,6 +34,7 @@
     "mcpd:deploy-dry": "bash deploy.sh --dry-run",
     "mcpd:logs": "bash logs.sh",
     "typecheck:pi-ext": "tsc -p src/pi-ext/tsconfig.json",
+    "typecheck:opencode-ext": "tsc -p src/opencode-ext/tsconfig.json",
     "smoke:clean": "tsx scripts/clean-smoke-resources.ts"
   },
   "engines": {
@@ -44,6 +45,11 @@
   "devDependencies": {
     "@earendil-works/pi-ai": "^0.84.1",
     "@earendil-works/pi-coding-agent": "0.84.1",
+    "@opencode-ai/plugin": "1.18.15",
+    "@opencode-ai/sdk": "1.18.15",
+    "@opentui/core": "0.4.5",
+    "@opentui/keymap": "0.4.5",
+    "@opentui/solid": "0.4.5",
     "@types/node": "^25.3.0",
     "@typescript-eslint/eslint-plugin": "^8.56.0",
     "@typescript-eslint/parser": "^8.56.0",
@@ -51,6 +57,7 @@
     "eslint": "^10.0.1",
     "eslint-config-prettier": "^10.1.8",
     "rimraf": "^6.1.3",
+    "solid-js": "^1.9.14",
     "tsx": "^4.21.0",
     "typebox": "1.3.11",
     "typescript": "^5.9.3",