RFC mismatch: fallback when missing local CLI

[liangmiQwQ]

vite-plus/rfcs/exec-command.md

Lines 259 to 261 in 2e9fe70

	### 1. Unconditional Delegation (No Global CLI Fallback)
	**Decision**: The global CLI always delegates `exec` to the local CLI. There is no fallback path for projects without vite-plus as a dependency.

vite-plus/rfcs/exec-command.md

Line 209 in 2e9fe70

The global CLI always delegates `exec` to the local CLI — there is no fallback path or direct execution in the global CLI. This follows the same unconditional delegation pattern as other Category C commands.

RFCs defines that Vite+ should have no fallback (fail) when vite-plus is missing when running in a project.

However, Vite+ currently uses VP_HOME/current/node_modules/vite-plus when the project has no vite-plus dependency, which is against with RFC.

IMO, I think a good enhancement is to warn when the project misses vite-plus dependency. It keeps the current behavior, only effect project calls, and improve UX / AX.

[fengmk2]

LGTM