chore: add SessionStart hook to install R + Octave for web sessions

Installs r-base-core (Drive-Box R drivers/tests) and octave (ETR torus
tests) in Claude Code on the web. Synchronous, idempotent, remote-only;
skips packages already present. Ada/Alire left out by design.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015hmgREHNsxYCuim33yUF2c

.claude/settings.json

@@ -0,0 +1,14 @@
+{
+  "hooks": {
+    "SessionStart": [
+      {
+        "hooks": [
+          {
+            "type": "command",
+            "command": "$CLAUDE_PROJECT_DIR/.claude/hooks/session-start.sh"
+          }
+        ]
+      }
+    ]
+  }
+}