fix(runner): alias params/input to args so tool implementations don't ReferenceError

Auth chain finally landed but tool calls crashed in the wetter server
with "Error: params is not defined". The MCP SDK passes the validated
tool args as a single parameter; our template names that parameter
`args` but the model frequently writes `params.location` / `input.x`
because that's how OpenAPI and JSON-RPC reference docs read.

Two-sided fix:
- render.ts wraps every implementation with `const params = args; const
  input = args;` inside the try block. Whichever alias the model
  picked, the variable resolves to the same validated object.
- SYSTEM_PROMPT now states the variable name EXPLICITLY ("variable
  named EXACTLY `args`, e.g. args.location") so new generations stop
  drifting on that detail.

Existing wetter runner needs a rebuild to pick up the alias shim.

apps/generator/src/lib/render.ts

@@ -38,6 +38,15 @@ function renderTool(tool: ToolSpec): string {
     inputSchema: ${schemaShape},
   },
   async (args) => {
+    // The MCP SDK passes the validated tool arguments as the single
+    // parameter. Models trained on OpenAPI / JSON-RPC examples reach
+    // for "params" instead of "args", and "input" shows up too — bind
+    // every common alias to the same object so the generated body
+    // works whichever name the model picked. Without this the runner
+    // crashes with "ReferenceError: params is not defined" at the
+    // first tool call (verified in prod with the wetter server).
+    const params = args;
+    const input = args;
     try {
       ${tool.implementation}
     } catch (err) {