feat: scratchpad tool + fix Claude auth token expiry warning

- Add cortex/tools/scratch.py with scratch_read/write/append/clear tools
- Register all four scratch tools in the orchestrator tool registry
- Create inara/SCRATCH.md as the backing file (never distilled/archived)
- Fix auth.py: expiresAt reflects short-lived access token (~8h) not the
  1-year refresh token — suppress expiry warning when refreshToken is present

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

cortex/tools/scratch.py

@@ -0,0 +1,79 @@
+"""
+Scratchpad tools for Inara.
+
+A lightweight, persistent notepad stored at inara/SCRATCH.md.
+Nothing here is ever distilled or archived — it is intentionally transient.
+Good for: working notes mid-task, half-formed ideas, things too long for
+a chat response but not worth saving to memory or a journal entry.
+
+Operations:
+  scratch_read    — return the full contents (or a message if empty)
+  scratch_write   — replace the entire scratchpad
+  scratch_append  — add a new timestamped section at the bottom
+  scratch_clear   — erase everything
+"""
+
+import asyncio
+from datetime import datetime, timezone
+from pathlib import Path
+
+from config import settings
+
+
+def _scratch_path() -> Path:
+    return settings.inara_path() / "SCRATCH.md"
+
+
+def _now_label() -> str:
+    return datetime.now(timezone.utc).strftime("%Y-%m-%d %H:%M UTC")
+
+
+# ---------------------------------------------------------------------------
+# Sync implementations
+# ---------------------------------------------------------------------------
+
+def _scratch_read() -> str:
+    p = _scratch_path()
+    if not p.exists() or not p.read_text().strip():
+        return "Scratchpad is empty."
+    return p.read_text()
+
+
+def _scratch_write(content: str) -> str:
+    _scratch_path().write_text(content.rstrip() + "\n")
+    return "Scratchpad updated."
+
+
+def _scratch_append(content: str, heading: str | None = None) -> str:
+    p = _scratch_path()
+    existing = p.read_text() if p.exists() else ""
+    label = heading or _now_label()
+    section = f"\n## {label}\n\n{content.strip()}\n"
+    p.write_text(existing.rstrip() + "\n" + section)
+    return f"Appended section: {label}"
+
+
+def _scratch_clear() -> str:
+    p = _scratch_path()
+    p.write_text("")
+    return "Scratchpad cleared."
+
+
+# ---------------------------------------------------------------------------
+# Async wrappers
+# ---------------------------------------------------------------------------
+
+async def scratch_read() -> str:
+    return await asyncio.to_thread(_scratch_read)
+
+
+async def scratch_write(content: str) -> str:
+    return await asyncio.to_thread(_scratch_write, content)
+
+
+async def scratch_append(content: str, heading: str | None = None) -> str:
+    return await asyncio.to_thread(_scratch_append, content, heading)
+
+
+async def scratch_clear() -> str:
+    return await asyncio.to_thread(_scratch_clear)