Default and Enterprise theme packs

Choose default-light.json, default-dark.json, enterprise-light.json or
enterprise-dark.json explicitly. Default preserves the current 8px base radius and
8px spacing base. Enterprise uses a 4px radius, 6px spacing base and stronger borders.
Both inherit the runtime palette, typography and any applicable builder-brand layer.
The files contain presentation tokens only; they do not change pages or permissions.

Custom designs should consume the runtime tokens rather than copying colors into
components. Per-placement comfortable/compact choices still select relative spacing
from the chosen theme. Selecting a pack replaces stored app-theme overrides; review
any previous custom overrides before saving.

Use the existing server-side BuildWithHQConnector.getTheme() and updateTheme() API.
Read the current theme/version when opening the editor and retain that version with
the user's draft. After the user explicitly confirms the selected pack, send only:

  {
    themeJson: chosenPack.themeJson,
    cssVariables: chosenPack.cssVariables,
    designTokensJson: chosenPack.designTokensJson,
    expectedVersion: versionShownToTheUser
  }

The outer file fields schemaVersion and themeKey are library metadata, not write
request properties. Never invent an installed templateThemeId. A conflict requires
reviewing the current theme and the user's draft; do not fetch a new version and
blindly retry. The routes remain GET/PUT /v1/apps/{saasAppId}/theme with their existing
themes.read/themes.write scopes and verified app-principal authority. A server-held
live app credential is required; never place it in browser code.

An explicit dark document requires the runtime selector-precedence fix shipped with
these source inputs. System-mode base colors continue to yield to the built-in dark
palette unless a supported dark override is present. Validate the installed runtime
and publish a newly versioned kit before claiming these packs are available to users.
Do not overwrite an existing immutable kit or change an installed template snapshot.
