chore: bump version to 2.4.0

Adapter plugin architecture, codebase review remediation (23 items),
4 complexity refactors, 180 new ML test coverage, CI hardening
(bandit SAST, SHA-pinned actions, uv audit), 73 pyright fixes,
web UI store restoration.

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

Author: NetDevAutomate

packages/studyctl/pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "studyctl"
-version = "2.3.0"
+version = "2.4.0"
 description = "AuDHD-aware study tool with AI Socratic mentoring, spaced repetition, and content pipeline"
 requires-python = ">=3.12"
 readme = "README.md"