refactor(hooks): replace direct output.args mutation with replaceToolArgs (question/webfetch/null-byte)

Replace Object.assign(output.args, truncatedArgs), output.args.url = resolution.url,
and output.args.command = ... .replace(/\x00/g, "") with replaceToolArgs() calls
in question-label-truncator, webfetch-redirect-guard, and plugin/tool-execute-before.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/hooks/webfetch-redirect-guard/hook.ts

@@ -1,5 +1,5 @@
 import type { PluginInput } from "@opencode-ai/plugin"
-import { log } from "../../shared"
+import { log, replaceToolArgs } from "../../shared"
 import {
   MAX_WEBFETCH_REDIRECTS,
   WEBFETCH_REDIRECT_ERROR_PATTERNS,
@@ -85,7 +85,7 @@ export function createWebFetchRedirectGuardHook(_ctx: PluginInput) {
         })
 
         if (resolution.type === "resolved") {
-          output.args.url = resolution.url
+          replaceToolArgs(output, { url: resolution.url })
           return
         }