release: bump to 0.2.4

[mashware]

What

Version bump 0.2.3 → 0.2.4 across the workspace (root + server/web/cli package.json, internal dependency pins, package-lock.json) and server.json (.version and .packages[].version).

Ships the accumulated work since 0.2.3:

• opt-in pre-push reminder for unconsolidated staging (feat(cli): opt-in pre-push reminder for unconsolidated staging #3)
• "What this is" concept section in the README (docs(readme): add "What this is" concept section #4)
• possible-contradiction candidates surfaced in doctor (feat: surface possible-contradiction candidates in doctor #5)
• publishing to the MCP Registry on version tags (feat: publish to the MCP Registry on version tags #6)

After merge

Pushing the tag v0.2.4 against main triggers the release workflow, which publishes the three npm packages and the server metadata to the MCP Registry (versions synced to the tag). The tag push is intentionally a manual, deliberate step.

Verification

All versions consistent at 0.2.4, no stale 0.2.3 refs in the lockfile, build clean, tests green (CLI/server/web). server.json validated against the official schema and the live registry (mcp-publisher validate) in the prior PR.