fix: enforce workspace isolation to prevent agent pollution (#57) (#72)

Problem: After installing Agent Reach, agents may clone repos, create
files, or write output into the workspace directory, gradually polluting
the user's project. Over time this degrades the agent experience.

Fix:
- SKILL.md: add Workspace Rules section — never create files in workspace
- install.md: add Directory Rules table, explicit boundary about workspace
- install.md: all git clone commands now target ~/.agent-reach/tools/
- update.md: add workspace warning
- cli.py: install creates ~/.agent-reach/tools/ directory

All agent-facing docs now enforce: /tmp for temp, ~/.agent-reach/ for
persistent data, workspace stays untouched.

Co-authored-by: Panniantong <panniantong@users.noreply.github.com>

agent_reach/cli.py

@@ -147,6 +147,10 @@ def _cmd_install(args):
     print("👁️  Agent Reach Installer")
     print("=" * 40)
 
+    # Ensure tools directory exists (for upstream tool repos)
+    tools_dir = os.path.expanduser("~/.agent-reach/tools")
+    os.makedirs(tools_dir, exist_ok=True)
+
     if dry_run:
         print("🔍 DRY RUN — showing what would be done (no changes)")
         print()