Fonts: carry uploaded faces through export/import + embed in SVG export

docs/spec/09-data-model.md

@@ -100,6 +100,7 @@ Some preferences persist independently of _UserSettings_ so they can update freq
 | Snippet store          | All _Snippet_ records                             | Local, with a practical budget of about 5 MB. A storage monitor tracks usage and surfaces warnings as the budget fills (see _Snippet Library_). |
 | Dataset store          | All _Dataset_ records                             | Local, in a separate, much higher-capacity store, suited to larger payloads.                                                                    |
 | Theme store            | All _CustomTheme_ records (G)                     | Local, separate store; records are small (a config object plus metadata).                                                                       |
+| Font store             | All _FontAsset_ records (H)                       | Local, separate store; holds raw font-file bytes, so it is sized like the dataset tier (per-face cap ~10 MB).                                   |
 | Settings & preferences | _UserSettings_ plus the app/UI preferences in (D) | Local, small.                                                                                                                                   |
 
 Everything stays in the browser — no server or account is involved. All tiers survive reload and function offline. Because capacity is finite and per-browser, _Import & Export_ is the supported path for backup and for moving data between browsers or devices.
@@ -127,3 +128,23 @@ A **CustomTheme** is a user-named Vega-Lite config saved in the library and offe
 | `modified` | ISO-timestamp string | When the theme was last changed.                                                              |
 
 Selection is keyed by `id` (not name) so renaming a theme never invalidates the persisted `ui.chartTheme`. A persisted `custom:<id>` whose record no longer exists is not an error: charts render with the house style until the record appears (themes hydrate asynchronously), and deleting the actively-selected theme resets the selection to `astrolabe` explicitly. Custom themes travel in the _Import & Export_ envelope alongside snippets and datasets (spec §08).
+
+## H. FontAsset
+
+A **FontAsset** is a user-uploaded font face stored once and reused across themes and snippets. It is added and managed in the _Theme Builder → Type_ panel (see _Live Preview_), and referenced from a config's font slots by its `family` — exactly as a dataset is referenced by name. The raw bytes are registered as a live `FontFace` so a chart measures and renders the real face.
+
+| Field      | Type                       | Meaning                                                                                                                       |
+| ---------- | -------------------------- | ----------------------------------------------------------------------------------------------------------------------------- |
+| `id`       | number                     | Unique numeric identifier (store key).                                                                                        |
+| `version`  | number                     | Schema version of this record, for read-time migration (see _Schema versioning_ above).                                       |
+| `family`   | string                     | Unique CSS family name — the key configs reference (case-insensitive uniqueness, like datasets/themes).                       |
+| `data`     | bytes                      | The raw font-file bytes (registered as a `FontFace`). In an export envelope these are **base64-encoded** (spec §08).          |
+| `format`   | `woff2`/`woff`/`ttf`/`otf` | Container format, from the file extension.                                                                                    |
+| `fileName` | string                     | Original file name, kept for display and provenance.                                                                          |
+| `source`   | `file`/`google`            | Provenance. Only `file` (an upload) ships today; `google` is reserved for a later keyless-catalog tier.                       |
+| `axes`     | array, optional            | Variation axes for a variable font (parsed from `fvar`); drives the `FontFace` weight/width ranges. Absent for a static face. |
+| `size`     | number                     | Byte length of `data`.                                                                                                        |
+| `created`  | ISO-timestamp string       | When the font was first added.                                                                                                |
+| `modified` | ISO-timestamp string       | When the font was last changed (e.g. renamed).                                                                                |
+
+A font is identified by its `family`. No theme or snippet stores a font field: the faces a config uses are derived by scanning its font slots (the config is the source of truth), so a snippet can use a font with no theme to carry it. Fonts travel in the _Import & Export_ envelope alongside snippets, datasets, and themes; on import a family clash **skips** the incoming face rather than renaming it (spec §08 → Name conflicts).