ci(workflow-linter): scope uses: grep to require leading whitespace (#24)

The in-tree workflow-linter.yml ran `grep -rn "uses:"` across
workflow files, which matched its own comment lines (`# Pattern:
uses: ...`) and shell command lines, causing a self-referential
false positive.

Fix: require leading whitespace before `uses:` (matches
standards/governance-reusable.yml line 640 pattern).

Author: hyperpolymath