Redesign the Storage Monitor as a storage-composition breakdown (snippets · datasets · app)

docs/spec/02-snippet-library.md

@@ -87,9 +87,10 @@ New snippets get a sensible default name, and a tag field exists on each snippet
 
 ## Storage Monitor
 
-A small indicator at the bottom of the library shows how much of the snippet storage budget is in use, warning the user before they run out of room. This concerns snippet storage specifically; datasets are stored separately with far greater capacity (see _Datasets_ / _Data Model_).
+A small indicator at the bottom of the library shows what the app's local storage is **made of** — a compact breakdown of how much space is taken by **snippets**, by **datasets**, and by the **app itself** (its offline-cached code and assets). It is informational: it helps the user see where space is going, not a fuel gauge counting down to a limit.
 
-- Displays current usage against the total budget (used vs. total), where the practical snippet budget is about 5 MB.
-- A fill indicator reflects the percentage used.
-- The indicator enters escalating warning states as usage climbs (a cautionary state past roughly 80% and a critical state past roughly 95%).
-- When storage is full, a save may fail; the system warns the user that the snippet could not be saved rather than silently losing data, so the user can delete snippets to free space.
+- The indicator stays **hidden until the user's own data — snippets + datasets — reaches a meaningful size** (about 10 MB). Below that there is nothing worth managing, so it adds no clutter; the app's own cached footprint does not count toward this threshold.
+- When shown, the breakdown is a single proportional bar plus a labelled legend giving each category's size; meaning never rests on colour alone.
+- There is **no "X of Y free" figure**. Browsers report only an unreliable, padded storage _quota_, so a precise "free space" number would mislead; the app shows real measured sizes instead.
+- Snippet and dataset sizes are always shown — the app measures them directly. The **app** portion is shown when the browser exposes an overall usage figure; when it does not, the breakdown simply omits it.
+- The genuine "out of room" moment is handled where it happens: if a save fails because storage is full, the system warns that the snippet could not be saved rather than silently losing data, so the user can delete snippets or datasets to free space (see _Import & Export_ error handling).