fix(aztec-up): validate semver in uninstall to prevent path traversal

[nchamo]

Problem

aztec-up uninstall passes user input directly into an rm -rf path without validating the format:

rm -rf "$AZTEC_HOME/versions/$version"

The existing is_version_installed guard checks [ -d "$AZTEC_HOME/versions/$version" ], but this passes for path-traversal inputs like ../ because $AZTEC_HOME/versions/../ resolves to $AZTEC_HOME/ which is a valid directory.

This means aztec-up uninstall ../ executes rm -rf "$AZTEC_HOME/", deleting the entire Aztec home directory including all installed versions, the current symlink, and shared binaries like aztec-up itself.

Fix

Added a semver validation check using the existing is_semver function before the rm -rf is reached. Since installed version directories are always named with concrete semver strings (aliases like nightly are resolved to semver at install time), this rejects any input that isn't a valid version -- including path traversal attempts, typos, and other malformed strings.

The check is placed after is_version_installed so that the more user-friendly "not installed" message is shown first for valid-looking versions that simply aren't present.

Fixes F-484

[AztecBot]

✅ Successfully backported to backport-to-v4-next-staging #21899.