FN-6748: add Air dashboard theme

Adds a minimal, borderless Air color theme across dashboard theme selection and bootstrap validation.

- Register Air in the core theme union, dashboard theme options, and browser/desktop bootstrap validators.
- Add dark and light Air token blocks with flattened chrome styling and matching swatch samples.
- Cover Air registration and CSS invariants with a focused dashboard test.
- Document the Air theme alongside the existing Shadcn theme in dashboard theming guidance.

Files changed:
 docs/dashboard-guide.md                            |   2 +-
 packages/core/src/types.ts                         |   2 +
 packages/dashboard/app/__tests__/air-theme.test.ts |  58 ++++++++++++
 .../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       | 101 +++++++++++++++++++++
 packages/desktop/src/renderer/index.html           |   1 +
 8 files changed, 179 insertions(+), 2 deletions(-)

Fusion-Task-Id: FN-6748

Fusion-Task-Lineage: a0caf14f-673d-485c-8886-97e4b273b624

docs/dashboard-guide.md

@@ -1266,7 +1266,7 @@ Non-Command-Center dashboard CSS uses `--text` as the canonical primary text tok
 
 ### Theme system
 
-Dark/light modes via `data-theme`; 56 color themes via `data-color-theme` (lazy-loaded from `app/public/theme-data.css`), including the Shadcn zinc-neutral theme.
+Dark/light modes via `data-theme`; 57 color themes via `data-color-theme` (lazy-loaded from `app/public/theme-data.css`), including the Shadcn zinc-neutral theme. Air is the minimal, borderless, paper-like preset with near-monochrome tokens and CSS-only chrome flattening.
 
 - **Base tokens** (`--bg`, `--surface`, etc.) — redefine in `:root`, `[data-theme="light"]`, and every theme block.
 - **Semantic tokens** (`--autopilot-pulse`, `--event-error-text`, `--badge-mission-*`, `--fab-*`) — `:root` + `[data-theme="light"]` only; no per-color-theme overrides.