feat(webui): vue admin panel source

Vue 3 + TypeScript + Pinia + Tailwind v4 + shadcn-vue + Chart.js admin
panel source under webui/, built with Vite. Views: Overview (providers,
redis/cache/retry status, model aliases), Usage (per-user/per-group/total
tables with tokensIn/tokensOut/cost + limits), Charts (scope selector,
req/tokens(stacked in-out)/cost metric tabs, 24h/30d/12mo window
switcher, fed by GET /admin/api/usage/history). Pinia stores: auth
(sessionStorage key gate, x-api-key header, 401/403 re-prompt),
dashboard (5s poll), history (fetch-on-selection + 30s refresh).

Design: deliberate neutral warm-neutral palette with a signature teal
accent (no default Inter/purple-gradient/glassmorphism), real
typographic hierarchy via the platform UI/mono font stacks (zero
external assets - no Google Fonts), dark+light via prefers-color-scheme
(no class toggle, no theme switcher). Charts: zero-based bars, honest
axes, Okabe-Ito colorblind-safe series, tokens-in/out as a
distinguishable stacked pair.

vite.config.ts: base '/admin/' (matches admin.go's route layout) and
build.modulePreload.polyfill:false (no inline bootstrap script, so the
tightened admin CSP needs no 'unsafe-inline'). Code-split: Chart.js
(ChartsView) loads lazily, not in the initial bundle.

generate.mjs reads dist/ after `vite build` and writes
../admin_assets_gen.go (not committed by this change) - base64-encodes
every asset, decoded once at package-var init; documented rationale in
the script's own header comment.

Hygiene: webui/go.mod walls webui/ off from the repo root's `go build`/
`vet`/`test ./...` (npm's node_modules bundles a stray .go file that
would otherwise be swept in); tools/yaegi-check/main.go excludes webui/
from its GOPATH copy for the same reason. webui/ export-ignored
(.gitattributes) from release source tarballs; webui/node_modules/
gitignored. tsconfig.app.json/tsconfig.node.json's JSONC comments
dropped (TS itself is fine with either; the global pre-commit JSON
validator is not) - no config values changed.

tools/yaegi-check/main.go

@@ -56,6 +56,15 @@ const (
 // needs, and copying its "go.yaml.in"-style nested module dirs into a
 // module-less GOPATH tree would otherwise confuse Yaegi's own import
 // resolution) have nothing to do with the plugin package Yaegi imports.
+// webui/ (Vue admin-panel task) is excluded for the same reason vendor/
+// is: its own go.mod already walls it off from the repo root's `go
+// build`/`vet`/`test ./...`, and its node_modules tree — hundreds of MB,
+// including a stray bundled .go file
+// (node_modules/flatted/golang/pkg/flatted.go) — would otherwise both
+// balloon copyRepoSource's wall time and risk Yaegi tripping over code
+// this repo neither wrote nor can build. The plugin only ever imports the
+// generated admin_assets_gen.go at the repo root, never anything under
+// webui/ itself.
 var excludedTopLevelDirs = map[string]bool{
 	"tools":        true,
 	"integration":  true,
@@ -63,6 +72,7 @@ var excludedTopLevelDirs = map[string]bool{
 	"docs":         true,
 	".git":         true,
 	"vendor":       true,
+	"webui":        true,
 }
 
 func main() {