docs: mark launch as opt-in plugin in root README (DX-9744)

[harshitha-cstk]

What

Removes the inline launch command sections and TOC entries from the bundled CLI root README (packages/contentstack/README.md) and replaces them with a short note explaining that launch is provided by the opt-in @contentstack/cli-launch plugin — not bundled — including the install command and a link to the plugin's GitHub README.

Why

Part of demoting launch to an opt-in plugin (DX-9742). Scoped narrowly to the launch block only per the DX-9744 decision (TRD recommendation, to keep GA blast radius small). Other opt-in-plugin doc cleanups are intentionally deferred.

Notes

• This region sits inside the oclif <!-- commands --> markers, so a future oclif readme run will regenerate it and drop the note as long as @contentstack/cli-launch remains a dependency + oclif plugin in package.json. The durable fix (removing launch from package.json) is tracked under the parent demotion work (DX-9742).

Ticket: https://contentstack.atlassian.net/browse/DX-9744

🤖 Generated with Claude Code

[github-actions]

🔒 Security Scan Results

ℹ️ Note: Only vulnerabilities with available fixes (upgrades or patches) are counted toward thresholds.

Check Type	Count (with fixes)	Without fixes	Threshold	Result
🔴 Critical Severity	0	0	10	✅ Passed
🟠 High Severity	2	37	25	✅ Passed
🟡 Medium Severity	0	2	500	✅ Passed
🔵 Low Severity	0	0	1000	✅ Passed

⏱️ SLA Breach Summary

✅ No SLA breaches detected. All vulnerabilities are within acceptable time thresholds.

Severity	Breaches (with fixes)	Breaches (no fixes)	SLA Threshold (with/no fixes)	Status
🔴 Critical	0	0	15 / 30 days	✅ Passed
🟠 High	0	0	30 / 120 days	✅ Passed
🟡 Medium	0	0	90 / 365 days	✅ Passed
🔵 Low	0	0	180 / 365 days	✅ Passed

ℹ️ Vulnerabilities Without Available Fixes (Informational Only)

The following vulnerabilities were detected but do not have fixes available (no upgrade or patch). These are excluded from failure thresholds:

• Critical without fixes: 0
• High without fixes: 37
• Medium without fixes: 2
• Low without fixes: 0

✅ BUILD PASSED - All security checks passed