feat(agent): isolate from erik — dedicated overlord-agent user

The agent service was running as User=erik, which meant:
- Sessions polluted erik's ~/.claude/projects/
- erik's .claude/settings.local.json (months of accumulated dev permissions
  for docker/git/dotnet/etc.) was loaded by the production agent, defeating
  the --allowed-tools whitelist
- Subscription rate quota mingled between human-erik's interactive Claude
  Code use and the production assistant
- Theoretical access to /home/erik/.ssh, .bash_history, .gitconfig

Now:
- User=overlord-agent (system account, no shell, /var/lib/overlord-agent home)
- HOME=/var/lib/overlord-agent — claude state fully isolated from erik
- /home/erik/.claude permissions tightened to 0700 (was 0755)
- group=overlord-agent on the repo + /etc/overlord/agent.env (read-only)

Project settings:
- New strict committed .claude/settings.json: deny Bash/Read/Write/Edit/
  Glob/Grep/NotebookEdit/WebSearch; allow only WebFetch(domain:acpedia.org)
- .claude/settings.local.json now gitignored (was leaking dev permissions
  to the server through the deploy)

agent/overlord-agent.service

@@ -5,18 +5,23 @@ Wants=network-online.target
 
 [Service]
 Type=simple
-User=erik
-Group=erik
-# Working directory MUST be the repo root so:
-#   - claude -p sessions land at ~/.claude/projects/-home-erik-MosswartOverlord/
-#   - .mcp.json is auto-loaded
+# Dedicated unprivileged user — kernel-level isolation from `erik`.
+# overlord-agent has NO access to /home/erik/.claude (mode 0700),
+# /home/erik/.ssh, /home/erik/.bash_history, /home/erik/.gitconfig, etc.
+# Its own claude state lives at /var/lib/overlord-agent/.claude/ and its
+# claude session JSONLs land there — completely separate from any
+# interactive Claude Code use by the human user.
+User=overlord-agent
+Group=overlord-agent
+# Working directory: the repo root (group-readable to overlord-agent).
+# claude session JSONLs path-encode this cwd so it's important to keep
+# stable across restarts.
 WorkingDirectory=/home/erik/MosswartOverlord
-# Secrets moved OUT of /home/erik/ to /etc/overlord/agent.env so
-# ProtectHome=read-only blocks their read entirely. The file is
-# root-owned, mode 0640, group=erik.
+# HOME explicitly set so claude reads /var/lib/overlord-agent/.claude/*
+# instead of trying /home/erik/.claude/* (which is now 0700, locked out).
+Environment="HOME=/var/lib/overlord-agent"
+# Secrets file (root:overlord-agent 0640).
 EnvironmentFile=-/etc/overlord/agent.env
-# Backwards-compat: also try the old location during transition.
-EnvironmentFile=-/home/erik/MosswartOverlord/.env
 # Run inside the venv populated by install.sh.
 ExecStart=/home/erik/MosswartOverlord/agent/.venv/bin/python -m agent.service
 Restart=on-failure
@@ -37,12 +42,11 @@ ProtectHome=read-only
 # Allow writing only to the explicit paths claude / our service need.
 # - ~/.claude — session JSONL files
 # - .venv pycache — minor pip cache writes
-ReadWritePaths=/home/erik/.claude
+ReadWritePaths=/var/lib/overlord-agent/.claude
 ReadWritePaths=/home/erik/MosswartOverlord/agent/.venv
 ReadWritePaths=/var/log/overlord-agent
-# Keep $HOME visible to the venv python so it can find pip cache etc.
-# (read-only via ProtectHome=read-only — this writable carve-out is
-# narrowly the .claude session dir above.)
+# StateDirectory creates/owns /var/lib/overlord-agent automatically.
+StateDirectory=overlord-agent
 LogsDirectory=overlord-agent
 LogsDirectoryMode=0755
 PrivateTmp=true