fix(dev): improve argument validation and fix filter typo in dev scripts

[alelpoan]

Fix three bugs in dev scripts that cause silent failures or incorrect behavior.

Changes:
register-enable-node.sh: missing argument count check causes unbound variable errors, added [[ $# -ne 4 ]] guard with usage and example
dev/gen/migration: missing $1 check allows empty migration name to be passed to migrate create, added guard with usage and example
dev/test: 'pkg/mock' → 'pkg/mocks' — filter never matched real path, causing mock packages to be included in test runs

Test plan:

• ./dev/cmd/register-enable-node.sh with no args prints usage and exits cleanly
• ./dev/gen/migration with no args prints usage and exits cleanly
• dev/test now correctly excludes pkg/mocks packages from test runs

Note

Fix filter typo and add argument validation to dev scripts

• Adds argument count validation to register-enable-node.sh, printing usage and exiting with status 1 when exactly 4 arguments are not provided.
• Adds missing-argument validation to the migration script, requiring a migration name before invoking the go migrate tool.
• Fixes a grep exclusion typo in the test runner, changing pkg/mock to pkg/mocks so the correct packages are excluded when generating the test package list.

^{Macroscope summarized 0b724a5.}