chore: clean up clear-cut ESLint warnings (#732) (#734)

Pay down pre-existing error→warn lint debt. Removes dead imports/vars, unused functions, redundant regex/string escapes, and stale eslint-disable directives; converts unused `catch (_e)` to optional catch binding (src/*.cts).

No behavior change. Lint 345→125 warnings (0 errors); deferred categories (n/no-process-exit, test-sleeps, control-regex) tracked in #732 for follow-up. Full test suite green (0 failures); code-review verified all removals unused and all escape fixes semantics-preserving.

Closes #732

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

src/graphify.cts

@@ -33,7 +33,7 @@ function isGraphifyEnabled(planningDir: string): boolean {
       (config.graphify as Record<string, unknown>).enabled === true
     ) return true;
     return false;
-  } catch (_e) {
+  } catch {
     return false;
   }
 }
@@ -230,7 +230,7 @@ function safeReadJson(filePath: string): Graph | null {
   try {
     if (!fs.existsSync(filePath)) return null;
     return JSON.parse(fs.readFileSync(filePath, 'utf8')) as Graph;
-  } catch (_e) {
+  } catch {
     return null;
   }
 }