fix(react-ui): stop false "unknown key" warnings for valid *ChartPalette theme keys

[ankit-thesys]

Fixes #714

Background

Theming charts the typed way — createTheme({ defaultChartPalette: [...] }) passed to ThemeProvider's lightTheme/darkTheme — compiles cleanly but printed dev-console warnings on every boot, twice per palette key:

[OpenUI] Unknown theme key "defaultChartPalette".
[OpenUI] darkTheme contains unknown key "defaultChartPalette". It will be ignored. Use createTheme() for typo detection with suggestions.

The Theme type declares eight *ChartPalette keys (default/bar/line/area/pie/radar/radial/horizontalBar), but both validators derived their allow-list from Object.keys(defaultLightTheme) (ThemeProvider.tsx:112, utils.ts:70), and the default themes define none of those keys — so every valid palette key tripped "unknown key". A runtime probe through the real ThemeProvider → useTheme() → useChartPalette chain showed the warning text was wrong: the theme merge spreads user overrides wholesale, so the palettes were never ignored — charts applied them all along, including the fallback to defaultChartPalette for unset chart types. Dev-only noise, but convincing enough that a downstream consumer abandoned theme-level palettes for per-chart customPalette workarounds.

Goal

Make the typed chart-palette API usable without false warnings, keep typo detection for genuinely unknown keys, and ensure the type-vs-runtime drift that caused this cannot silently recur.

What this PR does

• Introduces a single shared allow-list: KNOWN_THEME_KEYS = Object.keys(defaultLightTheme) + CHART_PALETTE_KEYS, consumed by both createTheme() and the ThemeProvider prop validator (previously two independent copies).
• Guards CHART_PALETTE_KEYS with satisfies Record<keyof ChartColorPalette, true>, so adding or removing a palette key on the type without updating the allow-list is a compile error.
• Deliberately adds no palette defaults to defaultTheme.ts: a default palette would shadow the per-chart theme prop fallback in useChartPalette, and themeToCssVars filters to string values, so array palettes never belonged in CSS vars anyway.
• Adds regression tests (ThemeProvider/__tests__/ThemeProvider.test.tsx) plus tsconfig.test.json (required by the ESLint override for __tests__ files, mirroring react-headless), and updates the ThemeProvider AGENTS.md with the palette-key exception to the "adding a new token" recipe.

Outcome

Re-ran the exact pre-fix reproduction probe against this branch:

	Before (main)	After (this PR)
Warnings on mount	6 (2 per palette key)	0
theme.barChartPalette in context	present	present (unchanged)
Chart colors from theme palette	applied	applied (unchanged)
Typo detection (defaultChartPalete)	warns	still warns, now suggests defaultChartPalette

Verification:

• pnpm --filter @openuidev/react-ui run test — 13/13 pass (7 new: allow-list covers every declared palette key + every default-theme key; createTheme silent for all 8 palette keys; ThemeProvider props silent for palette keys; genuine unknown keys still warn with suggestion; palettes flow theme → useTheme() → useChartPalette incl. defaultChartPalette fallback)
• pnpm --filter @openuidev/react-ui run typecheck — clean
• pnpm --filter @openuidev/react-ui run lint:check — 0 errors (pre-existing warnings only)
• pnpm --filter @openuidev/react-ui run format:check — clean