feat(server): introduce Zod request validation, starting with MCP tools

Adds Zod as the validation library for apps/server (in place of
express-validator), scoped here to a low-risk slice rather than a
full migration:

- MCP tool-call arguments (apps/server/src/api-mcp) are now validated
  end to end. Every tool's inputSchema is generated from its Zod
  schema via z.toJSONSchema() instead of hand-maintained JSON Schema
  literals, and every handler now parses its arguments before use —
  previously every handler did an unchecked `args as SomeType` cast
  with no runtime validation at all.
- A new validate.ts middleware (validateBody/validateParams) replaces
  the express-validator chokepoint for two reference routers, session
  and url-presets, demonstrating the pattern the remaining ~11 routers
  will follow in later PRs.
- An oxlint no-restricted-imports guardrail keeps zod importable only
  from apps/server, so it can never leak into the apps/client bundle.

The bulk of the REST router migration (automation, rundown, and the
rest of api-data) is intentionally left for follow-up PRs to keep this
change reviewable.

apps/server/package.json

@@ -22,7 +22,8 @@
     "osc-min": "2.1.2",
     "sanitize-filename": "^1.6.3",
     "ws": "^8.18.0",
-    "xlsx": "^0.18.5"
+    "xlsx": "^0.18.5",
+    "zod": "catalog:"
   },
   "devDependencies": {
     "@types/cookie-parser": "1.4.10",