Add edit/delete history, named sessions, scroll fix, systemd service

- Edit/delete individual messages from session context with inline editing
  (Ctrl+Enter saves, Escape cancels); changes sync to backend via PUT /history
- PUT /history/{session_id} endpoint to replace full message list
- Named sessions: readable slugs (e.g. quiet-spring) instead of UUID fragments
- Scroll no longer snaps to bottom when user has scrolled up to read history
- cortex.service: systemd unit for auto-start and restart-on-failure

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

cortex/session_store.py

@@ -1,9 +1,46 @@
 import json
+import random
 from pathlib import Path
 from datetime import datetime
 from config import settings
 
 
+_ADJECTIVES = [
+    "amber", "azure", "bold", "bright", "calm", "cedar", "cobalt", "coral",
+    "crisp", "dusk", "ember", "fern", "frost", "gold", "hazy", "indigo",
+    "jade", "keen", "lark", "lunar", "maple", "misty", "noble", "north",
+    "oak", "onyx", "opal", "pine", "quiet", "raven", "ridge", "river",
+    "sage", "silver", "slate", "solar", "steel", "stone", "swift", "teal",
+    "timber", "vale", "velvet", "violet", "warm", "wild", "winter", "wren",
+]
+
+_NOUNS = [
+    "bay", "bloom", "brook", "canyon", "cave", "cliff", "cloud", "coast",
+    "creek", "dale", "dawn", "delta", "dune", "echo", "falls", "field",
+    "fjord", "flare", "glade", "glen", "grove", "harbor", "haven", "hill",
+    "hollow", "isle", "lake", "ledge", "marsh", "meadow", "mist", "moon",
+    "moor", "peak", "plain", "pond", "reef", "ridge", "rise", "rock",
+    "shore", "sky", "slope", "spring", "star", "storm", "trail", "vale",
+    "wave", "wood",
+]
+
+
+def generate_session_id() -> str:
+    """Return a readable slug like 'amber-lake' or 'amber-lake-03'."""
+    existing = {s["session_id"] for s in list_all()}
+    for _ in range(30):
+        base = f"{random.choice(_ADJECTIVES)}-{random.choice(_NOUNS)}"
+        if base not in existing:
+            return base
+        # Try with a numeric suffix
+        candidate = f"{base}-{random.randint(2, 99):02d}"
+        if candidate not in existing:
+            return candidate
+    # Statistically unreachable for a personal tool
+    import uuid
+    return str(uuid.uuid4())[:8]
+
+
 def _path(session_id: str) -> Path:
     d = settings.sessions_path()
     d.mkdir(parents=True, exist_ok=True)