fix(dashboard): reject unknown operator actions - #7427

Summary

• treat workflow operator action descriptors as untrusted runtime data
• reject unknown string verbs and malformed provide_input objects before dereferencing them
• skip only an unsupported action while preserving the remaining authorized action buttons
• add focused regressions for unknown strings, malformed objects, and valid provide-input descriptors

Inventory finding: F-9855eab2ac16b385

Verification

• corepack pnpm@10.33.0 --dir crates/librefang-api/dashboard exec vitest run src/components/OperatorActionBar.test.ts (3 passed)
• corepack pnpm@10.33.0 --dir crates/librefang-api/dashboard test (102 files, 1078 tests passed)
• corepack pnpm@10.33.0 --dir crates/librefang-api/dashboard typecheck
• corepack pnpm@10.33.0 --dir crates/librefang-api/dashboard lint
• corepack pnpm@10.33.0 --dir crates/librefang-api/dashboard build
• git diff --check
• pre-commit and pre-push hooks

Out of scope

• validating operator action descriptors at the API boundary
• adding UI copy for unsupported future action verbs
• changing the workflow operator action schema