feat(packages): add dsh-plugin-browserskill — DeepSeek Harness tools for bsk

Add a new monorepo package that registers BrowserSkill (bsk) browser
automation as model-visible tools in DeepSeek Harness (dsh):

- 11 tools mapping to bsk CLI --json commands: session start/stop/list,
  navigate, snapshot, observe, click, fill, press, screenshot, emulate
- multi-session support: optional session arg with a current-session
  pointer, session id echoed in every result, configurable concurrency
  cap (default 5), and dispose-time cleanup of plugin-started sessions
- cancellation: exec.signal aborts kill the underlying bsk child process
- terminal-style UI cards (command line as the call card, output as the
  result card); screenshots inline the PNG through the host attachment
  store when the model route accepts image input, else return the path
- config: bskPath / defaultTimeoutMs / maxSessions via Schemastery schema
- install guidance when the bsk binary is missing; bsk JSON error
  envelopes (code/message/hint) surfaced to the model
- unit tests mock the bsk runner (no real browser required); the root
  lint script now also runs the package's typecheck + tests so the
  existing CI frontend job covers the new package (a dedicated CI job
  diff is provided in the PR; the pushing token lacks workflow scope)

package.json

@@ -9,7 +9,7 @@
     "ext:dev": "pnpm --filter @browser-skill/extension dev",
     "ext:test": "pnpm --filter @browser-skill/extension test",
     "vom:test": "pnpm --filter @browser-skill/vom test",
-    "lint": "biome check . && stylelint \"**/*.css\"",
+    "lint": "biome check . && stylelint \"**/*.css\" && pnpm --filter dsh-plugin-browserskill typecheck && pnpm --filter dsh-plugin-browserskill test",
     "format": "biome format --write ."
   },
   "devDependencies": {