Security: Replace unsafe read() calls with safer alternatives

Replaced unsafe use of read() function on user-controlled property values
to prevent arbitrary code execution vulnerability.

Changes:
- Lines 1353, 1406: Changed read() to string-to-number() for DRILL_CARD_WEIGHT
- Line 2838: Changed read() to string-to-number() for DRILL_LAST_INTERVAL
- Line 1068: Created org-drill--safe-read-learn-data() helper function that:
  * Uses read-from-string instead of read
  * Validates input is a list with at least 3 numeric elements
  * Returns nil on invalid/malicious input with error handling
  * Falls back to safe defaults if LEARN_DATA is corrupted

Impact: Prevents arbitrary code execution if attacker controls org-mode
properties through shared files or malicious imports.

Fixes severity A security bug in todo.org

0 files changed, 0 insertions, 0 deletions