docs: update README and CLI to reflect migration of Linux package repositoy from Cloudsmith

[victorvhs017]

Description 📣

• Added a notice in the README about the migration to artifacts-cli.infisical.com and the impending shutdown of Cloudsmith.
• Implemented a one-time daily notice in the CLI for users regarding the repository migration, including a link to the migration guide.
• Introduced caching for the migration notice to prevent repeated prompts within a 24-hour period.
• Added a manual test for the migration notice display functionality.

Type ✨

• Bug fix
• New feature
• Improvement
• Breaking change
• Documentation

---

• I have read the contributing guide, agreed and acknowledged the code of conduct. 📝

[infisical-review-police]

💬 Discussion in Slack: #pr-review-cli-265-docs-update-readme-and-cli-to-reflect-migration-of-linux-packa

Posted by Review Police — reviews, comments, new commits, and CI failures will stream into this channel.

[greptile-apps]

Greptile Summary

This PR adds a one-time-per-day migration notice (Go) and a README callout informing users that the Infisical CLI Linux package repository has moved from Cloudsmith to artifacts-cli.infisical.com. The caching mechanism, env-var opt-out, and integration into the root pre-run hook are all well-structured.

• README: The callout block contains two unfilled placeholders — **[DATE]** for the Cloudsmith shutdown date and [MIGRATION_GUIDE_URL] as the href — which will render literally on GitHub, producing a broken link and no actionable date.
• CLI notice: The migrationGuideURL constant is acknowledged in a TODO as a placeholder (https://infisical.com/docs/cli/usage is the general usage page, not a migration guide); users who follow the notice will land on an unrelated page.
• The cache, throttle logic, INFISICAL_DISABLE_MIGRATION_NOTICE escape hatch, and the manual test are correct and complete.

Confidence Score: 3/5

Not ready to merge — both the README and the CLI notice ship with placeholder URLs/dates that will be visible to users immediately on release.

The README will render a literal [DATE] and a broken markdown link ([migration steps]([MIGRATION_GUIDE_URL])), and the CLI notice directs users to the generic CLI usage page rather than any migration instructions. These are the two user-facing outputs the PR is meant to deliver, so both are broken as submitted.

README.md (unfilled placeholders) and packages/util/check-for-update.go (placeholder migration URL with unresolved TODO)

Important Files Changed

Filename	Overview
README.md	Adds a migration notice callout block, but two placeholders — [DATE] and [MIGRATION_GUIDE_URL] — are not filled in and will render literally on GitHub.
packages/util/check-for-update.go	Replaces the old apt-only banner with a cross-platform one-per-day migration notice backed by a JSON cache; the URL constant has an acknowledged TODO pointing to the wrong page.
packages/cmd/root.go	Wires DisplayPackageRepoMigrationNoticeWithWriter into the pre-run hook, correctly guarded by the existing !silent && !isStructuredOutput && !docker conditions.
packages/util/constants.go	Adds MIGRATION_NOTICE_CACHE_FILE_NAME constant; trivial, looks correct.
packages/util/migration_notice_manual_test.go	Adds a manual visual test that isolates HOME to a temp dir and exercises the notice display; straightforward and correct.

_{Reviews (1): Last reviewed commit: "Update README and CLI to reflect migrati..." | Re-trigger Greptile}