feat: add self-check tip to check output

[PascalThuet]

Summary

Closes #2573.

Keeps specify check as an offline environment scan and adds a discoverability tip for the existing specify self check version lookup.

Changes

• Add a specify self check tip to specify check output.
• Keep specify check network-free; no --latest option is added.
• Document the offline/version-check split in the core command reference and upgrade troubleshooting.
• Add tests that assert the tip is shown and that specify check does not call the latest-release lookup.

Validation

Local:

• uv run pytest tests/test_check_tool.py tests/test_upgrade.py -q
• uvx ruff check src/ tests/test_check_tool.py tests/test_upgrade.py
• git diff --check origin/main
• uv run specify check --help

CI:

• GitHub Actions will run the full PR validation suite.

AI Disclosure

• I did not use AI assistance for this contribution
• I did use AI assistance (describe below)

Used AI assistance to inspect the existing check/self-check flow, adjust the PR based on review feedback, add tests/docs, and run local validation. The changes were reviewed before submission.

[mnriem]

Thanks for the work here! We left a suggestion on #2573 — specify check is an offline environment scan and specify self check already owns the version-lookup logic. Rather than adding --latest with network code, we think a simpler tip line in specify check output would solve the discoverability problem without blurring the two commands' responsibilities:

Tip: Run 'specify self check' to verify you have the latest CLI version.

Would you be open to adjusting the PR in that direction?

[PascalThuet]

Updated in e886a15 based on the suggestion: removed the --latest approach, kept specify check network-free, added the specify self check tip, and updated docs/tests. Local validation passes: targeted pytest, ruff, and diff whitespace check.

[Copilot]

Pull request overview

Adds a discoverability tip to the specify check command output pointing users to specify self check for CLI version verification, while keeping specify check strictly offline. This also updates docs to clarify the offline vs. version-lookup split and introduces regression tests ensuring no latest-release lookup is triggered by specify check.

Changes:

• Print a specify self check tip at the end of specify check output.
• Document the intended separation: specify check (offline environment scan) vs. specify self check (version lookup).
• Add CLI-level tests that assert the tip appears and that latest-release lookup is not invoked.

Show a summary per file

File	Description
src/specify_cli/__init__.py	Adds the new self-check tip to the check() command output.
tests/test_check_tool.py	Adds CLI invocation tests validating tip presence and enforcing no latest-release lookup.
docs/reference/core.md	Clarifies specify check is offline and directs version checks to specify self check.
docs/upgrade.md	Adds troubleshooting guidance to run specify self check when behavior suggests an older CLI.

Copilot's findings

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• Files reviewed: 4/4 changed files
• Comments generated: 1