perf(cli): skip config runtime initialization when no config exists

[fengmk2]

vp check initializes Vite and Vitest to read metadata even when the selected workspace root has no vite.config.* file.

resolveUniversalViteConfig returns empty metadata when no supported config file exists. Otherwise, it passes the discovered path to Vite through configFile, which avoids a second filename search. resolveViteConfig loads define-config only when runtime resolution is necessary. Each call checks the filesystem, so later calls detect new config files. Existing configs retain runtime evaluation, plugin hooks, and error handling.

For vp check --fix on three TypeScript files, median elapsed time decreased by 14.8% (about 36 ms) without a config file.
The cases with a config file show no material performance change.

Case	Before: ac5fab0d6	After: 48d1c9247	Change
No config	242.2 ms	206.4 ms	-14.8%
Object literal config	367.9 ms	368.7 ms	+0.2%
defineConfig	374.2 ms	377.3 ms	+0.9%
Package directory with root config	366.9 ms	367.2 ms	+0.1%
Plugin config hook	364.2 ms	364.0 ms	≈0%
Lint fixes with config	380.7 ms	372.9 ms	-2.1%

For the no-config case, median /usr/bin/time -p real decreased from 0.24 s to 0.20 s.
The table uses a high-resolution wall clock; /usr/bin/time -p reports rounded values.

These local measurements used macOS arm64, an Apple M4 Max, Node 26.10.0, and the same release native binding.
Each variant ran in a fresh process with warm filesystem and Node compile caches.
The comparison used six warmups and fifteen measured rounds, with rotating execution order.
Identical-code controls differed from the baseline by at most 1.7% across these cases.

Related to #2698.

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