chore(#504): remove dead sdk/ references from eslint & stryker config

ADR-0174 retired @opengsd/gsd-sdk; sdk/ no longer exists. Removes the
sdkSrcExists guard + unused existsSync/join imports + sdk/dist/** ignore
from eslint.config.mjs, and drops the stale GENERATED comment + exclusion
for configuration.cjs (hand-authored since SDK removal) from stryker.config.mjs.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

eslint.config.mjs

@@ -3,8 +3,7 @@ import tseslint from 'typescript-eslint';
 import globals from 'globals';
 import pluginN from 'eslint-plugin-n';
 import noOnlyTests from 'eslint-plugin-no-only-tests';
-import { existsSync } from 'fs';
-import { join, dirname } from 'path';
+import { dirname } from 'path';
 import { fileURLToPath } from 'url';
 
 const __dirname = dirname(fileURLToPath(import.meta.url));
@@ -22,15 +21,12 @@ const localPlugin = {
   },
 };
 
-const sdkSrcExists = existsSync(join(__dirname, 'sdk', 'src'));
-
 export default tseslint.config(
   // ── Global ignores ─────────────────────────────────────────────────────────
   {
     ignores: [
       'node_modules/**',
       '**/dist/**',
-      'sdk/dist/**',
       '.worktrees/**',
       '.claude/**',
       'coverage/**',

stryker.config.mjs

@@ -23,7 +23,6 @@
 
 // Generated files that must NEVER be mutated
 const GENERATED_FILES = [
-  '!get-shit-done/bin/lib/configuration.cjs',   // GENERATED — sdk/src/config/index.ts
   '!get-shit-done/bin/lib/command-aliases.cjs',  // GENERATED
   '!get-shit-done/bin/lib/commands.cjs',         // GENERATED
   '!get-shit-done/bin/lib/core.cjs',             // GENERATED