FN-001: add Velvet dashboard color theme

Add the Velvet plum/burgundy theme across dashboard and desktop startup.

- Register Velvet in persisted theme options and pre-hydration validators
- Define dark/light palette tokens, selector swatch, and regression coverage
- Document the theme and add a minor CLI changeset

Files changed:
 .changeset/fn-001-velvet-theme.md                  |   6 ++
 docs/dashboard-guide.md                            |   5 +-
 docs/settings-reference.md                         |   2 +-
 packages/core/src/types/ui/execution-and-ui.ts     |   2 +
 .../dashboard/app/__tests__/velvet-theme.test.ts   | 101 +++++++++++++++++++++
 .../dashboard/app/components/ThemeSelector.css     |  14 +++
 packages/dashboard/app/components/themeOptions.ts  |   1 +
 packages/dashboard/app/index.html                  |   2 +-
 packages/dashboard/app/public/theme-data.css       |  86 +++++++++++++++++-
 packages/desktop/src/renderer/index.html           |   1 +
 10 files changed, 215 insertions(+), 5 deletions(-)

Fusion-Task-Id: FN-001
Fusion-Task-Lineage: a57d7458-b598-48e3-b4ed-cc082f32197d
Co-authored-by: Fusion <noreply@runfusion.ai>

docs/settings-reference.md

@@ -75,7 +75,7 @@ Defaults from `DEFAULT_GLOBAL_SETTINGS`; key scope from `GLOBAL_SETTINGS_KEYS`.
 |---|---|---:|---|
 | <a id="anthropicauthpreference"></a>`anthropicAuthPreference` | `"api-key" \| "subscription"` | `"api-key"` | Which Anthropic credential wins when BOTH a raw API key and a Claude subscription OAuth login are configured. `"api-key"` keeps the historical precedence; `"subscription"` moves the raw key below the OAuth steps so a stale or revoked saved key cannot shadow a working subscription (the `401 invalid x-api-key` failure mode). Global, because credentials live in the global `~/.fusion/agent/auth.json`. Never removes a source — with one credential configured, resolution reaches it under either value. Surfaced in Settings → Authentication, where the two Anthropic cards show which credential is in use; the control appears only when both are connected. |
 | `themeMode` | `"dark" \| "light" \| "system"` | `"system"` | Dashboard theme mode. Fresh installs follow the operating system light/dark preference until the user chooses Light, Dark, or System. |
-| `colorTheme` | `ColorTheme` | `"shadcn-ember"` | Dashboard color theme preset. Aurora is a built-in navy/teal/violet palette with a misty light counterpart; Calm is a low-stimulation slate/sage palette with a misty light counterpart; Dawn uses indigo/plum dark surfaces, amber accents, and dawn-white light surfaces; Midnight uses deep-navy surfaces with restrained violet/indigo accents and a cool pale light counterpart; Factory Dark uses graphite/steel surfaces, cool gunmetal borders, and restrained safety-orange accents with a concrete-gray light counterpart; Factory Light uses bright concrete/warm-white surfaces, steel-gray borders, a darkened safety-orange accent, and a warm-graphite dark counterpart. Use `"shadcn-custom"` to show the separate custom shadcn color picker in Settings → Appearance and the Command Center theme card. |
+| `colorTheme` | `ColorTheme` | `"shadcn-ember"` | Dashboard color theme preset. Aurora is a built-in navy/teal/violet palette with a misty light counterpart; Calm is a low-stimulation slate/sage palette with a misty light counterpart; Dawn uses indigo/plum dark surfaces, amber accents, and dawn-white light surfaces; Midnight uses deep-navy surfaces with restrained violet/indigo accents and a cool pale light counterpart; Velvet uses deep plum/burgundy dark surfaces with rose-gold accents and a warm blush-white light counterpart; Factory Dark uses graphite/steel surfaces, cool gunmetal borders, and restrained safety-orange accents with a concrete-gray light counterpart; Factory Light uses bright concrete/warm-white surfaces, steel-gray borders, a darkened safety-orange accent, and a warm-graphite dark counterpart. Use `"shadcn-custom"` to show the separate custom shadcn color picker in Settings → Appearance and the Command Center theme card. |
 | `shadcnCustomColors` | `Record<string, string>` | `undefined` | Optional shadcn design-token override map for `"shadcn-custom"` only. Keys are CSS token names such as `--accent`, `--bg`, `--surface`, `--card`, `--border`, `--text`, `--text-muted`, workflow status tokens, and `--color-success`/`--color-warning`/`--color-error`; values must be sanitized `#RGB` or `#RRGGBB` hex colors. Missing or invalid entries fall back to the `shadcn-custom` base defaults and are not applied to other themes. |
 | `language` | `"en" \| "zh-CN" \| "zh-TW" \| "fr" \| "es" \| "ko" \| "pt-BR"` | `undefined` | UI language for the dashboard and TUI. When unset, the dashboard detects from localStorage → browser language and the CLI from `--lang` flag → environment locale, falling back to `en`. Validated at the store write boundary (`validateLocale`); invalid values are dropped. Reset to auto-detect via the dashboard's "Auto" language option or `fn settings set language auto` (clears the persisted key). |
 | `dashboardFontScalePct` | `number` | `100` | Dashboard font scale percentage used by Appearance settings. Valid range: `85` to `125`; applied pre-hydration via document root font-size so board typography (column headers/counts, task cards, and quick-entry text) scales with the setting from first paint. |