feat(opencode): native opencode integration — /mcpctl switcher, live project switching, footer indicator

Adds `mcpctl config opencode`, two opencode plugins and an `opencode` skills
sync target, so an mcpctl project can be switched from inside opencode's TUI
and the active one is visible at a glance.

Unlike `config claude` / `config prime-agent`, this writes NO MCP entry into
the host's config. opencode exposes an HTTP API for its own MCP registry
(`POST /mcp`), so the project is mounted through the running app:

  - the token stays in ~/.mcpctl/opencode-state.json (0600) instead of a
    mode-0644 opencode.json users paste into bug reports;
  - switching projects takes effect on the next turn, with no restart.

Inside opencode:
  /mcpctl         filterable project picker; switches live
  /mcpctl-status  active project, mount state, gateway URL
  /mcpctl-skills  re-sync this project's skills
  plus a `mcpctl:<project>` indicator in the prompt footer, next to the model
  name and one line above the token counter.

Design notes:
  - the MCP server is registered under a constant name, so tools keep a stable
    `mcpctl_*` prefix and opencode's per-request tool resolution shows the new
    project's tools by itself — no "your old tool names are dead" message to
    the model, unlike the pi extension;
  - an unchanged mount is never re-registered: mcp.add rebuilds the connection
    and mcplocal binds a gated project's unlocked state to that connection's
    mcp-session-id, so re-adding would re-lock a project begin_session had just
    opened;
  - the server plugin does not mount during setup — setup runs before the
    server accepts connections and mcp.add calls back into it, which hangs
    opencode on a blank screen before the TUI draws;
  - the switcher shells out to this CLI (--skip-plugin --skip-marker) so token
    minting, state and skills stay in one place;
  - no usable credential aborts non-zero with the state file untouched, so a
    failed switch leaves the previous project working rather than swapping it
    for a mount that 401s.

`skills sync --agent opencode` installs into ~/.config/opencode/skill (XDG
aware) with the same shared-tree semantics as pi and prime-agent. The
credential plumbing shared with `config prime-agent` is lifted to one place and
parameterised by agent rather than copied.

The plugin sources are embedded in the CLI (generated, freshness-tested) so an
installed binary with no source tree can provision them, and are typechecked
against the real @opencode-ai/plugin types.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BVwuCjuMoA13gmzYEfcrNP

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 +45,10 @@
   "devDependencies": {
     "@earendil-works/pi-ai": "^0.84.1",
     "@earendil-works/pi-coding-agent": "0.84.1",
+    "@opencode-ai/plugin": "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 +56,7 @@
     "eslint": "^10.0.1",
     "eslint-config-prettier": "^10.1.8",
     "rimraf": "^6.1.3",
+    "solid-js": "1.9.12",
     "tsx": "^4.21.0",
     "typebox": "1.3.11",
     "typescript": "^5.9.3",