Added a dialog with each opportunity's details and releases

Every row has a details icon under the Find a Tender link. It opens a
dialog with the opportunity's details from the list, and fetches the
opportunity with its releases, shown as tabs, newest first. Each tab
summarises the release's tender, awards and contracts, links to its
Find a Tender notice where it is one, and has the release's JSON,
pretty-printed and highlighted, in a section laid out only when it's
opened.

The JSON is highlighted by splitting it into tokens shown as text, not
HTML, as releases come from outside sources. The README's saved
preferences now include the filters.

web/README.md

@@ -91,21 +91,28 @@ token when it first needs it, and a new one if a request is refused for it.
 - `src/primitives/createToasts.ts` – the toasts errors are shown in, bottom
   right, for 15 seconds or until dismissed
 - `src/lib/filterOpportunities.ts` – search and filter logic
-- `src/lib/opportunities.ts` – merging changed opportunities into the list
+- `src/lib/opportunities.ts` – merging changed opportunities into the list,
+  and Find a Tender notice links
+- `src/lib/ocdsRelease.ts` – what the details dialog reads from a release's
+  OCDS JSON
+- `src/lib/jsonTokens.ts` – splits JSON into tokens for highlighting
 - `src/components/` – FilterPanel, ClassificationPicker, OpportunityTable,
-  MarkMenu, ThemeToggle, ToastList; `styles.ts` holds shared Tailwind class
+  MarkMenu, OpportunityDialog (an opportunity's details), ReleaseTabs,
+  JsonView, ThemeToggle, ToastList; `styles.ts` holds shared Tailwind class
   strings
 
 Theme colours and the font are set in the `@theme` block of `src/index.css`.
 
 ## Saved preferences
 
-Two preferences are kept in the browser's localStorage (`src/lib/storage.ts`):
+Three preferences are kept in the browser's localStorage (`src/lib/storage.ts`):
 
 - `job_search.theme`: `light` or `dark`. If nothing is saved, the app follows
   the OS setting. A small script in `index.html` applies the saved theme
   before the first paint, so there's no flash.
 - `job_search.filtersOpen`: whether the filter panel is expanded.
+- `job_search.filters`: the filters, as JSON. A field that isn't valid is
+  read as its default.
 
 Dark mode works by swapping the colour tokens under `.dark` in
 `src/index.css`, so components don't need `dark:` variants.