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.

packages/llm/src/index.ts

@@ -15,7 +15,7 @@ Output ONE JSON object (no markdown, no prose, no code fences) with this exact s
       "inputSchema": {
         "param_name": { "type": "string|number|boolean|array|object", "description": "short", "required": true }
       },
-      "implementation": "async TS body, return { content: [{ type:'text', text:'...' }] }; secrets via process.env; HTTP via globalThis.fetch with AbortSignal.timeout(10000); try/catch -> { content:[{type:'text',text:'Error: ...'}], isError:true }; no eval/Function/child_process; no imports."
+      "implementation": "async TS body. The tool's validated arguments arrive in the variable named EXACTLY `args` (e.g. args.location, args.query). Return { content: [{ type:'text', text:'...' }] }. Secrets via process.env. HTTP via globalThis.fetch with AbortSignal.timeout(10000). Wrap external calls in try/catch and return { content:[{type:'text',text:'Error: ...'}], isError:true } on failure. No eval/Function/child_process. No import statements."
     }
   ],
   "resources": [],