fix: Windows shell robustness, project_root detection, and hook stdin safety (#1343)

Address 4 root causes of Windows + Claude Code reliability issues:

1. Workflow shell robustness: add || true guards to informational commands
   (ls, grep, find, cat) that return non-zero on "no results", preventing
   workflow step failures under strict execution models. Guard glob loops
   with [ -e "$var" ] || continue to handle empty glob expansion.

2. Hook stdin handling: replace readFileSync('/dev/stdin') with async
   process.stdin + timeout in agent templates (gsd-verifier.md). Existing
   JS hooks already have timeout guards.

3. project_root detection: fix isInsideGitRepo() to check .git at the
   candidate parent level (not just below it), enabling correct detection
   when .git and .planning/ are siblings at the same directory level —
   the common single-repo case from a subdirectory.

4. @file: handoff: add missing @file: handlers to autonomous.md and
   manager.md workflows that call gsd-tools init but lacked the handler
   for large output payloads.

Fixes #1343

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

get-shit-done/bin/lib/core.cjs

@@ -58,13 +58,15 @@ function findProjectRoot(startDir) {
   const root = path.parse(resolved).root;
   const homedir = require('os').homedir();
 
-  // Check if startDir or any of its ancestors (up to but not including a
+  // Check if startDir or any of its ancestors (up to AND including the
   // candidate project root) contains a .git directory. This handles both
-  // `backend/` (direct sub-repo) and `backend/src/modules/` (nested inside).
+  // `backend/` (direct sub-repo) and `backend/src/modules/` (nested inside),
+  // as well as the common case where .git lives at the same level as .planning/.
   function isInsideGitRepo(candidateParent) {
     let d = resolved;
-    while (d !== candidateParent && d !== root) {
+    while (d !== root) {
       if (fs.existsSync(path.join(d, '.git'))) return true;
+      if (d === candidateParent) break;
       d = path.dirname(d);
     }
     return false;