A Signal's own icon, from all of Font Awesome Free, searchable (#261)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/signals.md

@@ -16,6 +16,9 @@ their Signals that has not heard about the item yet.
   #256). It is closed or open as an OPML's folder is, remembered in each browser. A + at the right
   of the folder's row opens New signal. Inside the folder are the person's Signals, each with its
   words under its name and its unread count.
+- **An icon of its own** (#261), chosen in the Signal's dialog from all of Font Awesome Free 7.3.1,
+  the set the page's own icons come from: 2,883 icons, solid, regular and brands, searched by name
+  and Font Awesome's search terms ("ai" finds the robot). Without one, a Signal shows its initials.
 - **The folder's page** lists the Signals, as an OPML's page lists its feeds, with a + of its own.
 - **A Signal's page** is an ordinary item list: All, Unread, Downloaded and Pinned, search and sort.
   Its header says what it listens for (the sentence, or the words), and that nothing is picked
@@ -190,8 +193,10 @@ up to 500 characters. Anything else is a `400` saying so.
 ### `PATCH /api/signals/{id}`
 
 Any of the three: `{ "name": "F1" }`, `{ "keywords": ["f1", "grand prix"] }`,
-`{ "description": null }` (null or empty clears it). Any change drops the Signal's verdicts and
-wakes the judge, since each is part of the question. Answers `204`, or `404` for a Signal that is not yours.
+`{ "description": null }` (null or empty clears it), `{ "icon": "solid/robot" }`. A change to the
+name, words or sentence drops the Signal's verdicts and wakes the judge, since each is part of the
+question; a new icon does not. The page sends only what changed. An icon is `solid/`, `regular/` or
+`brands/` and a plain name, since the page puts it into an address: anything else is a `400`. Answers `204`, or `404` for a Signal that is not yours.
 
 ### `DELETE /api/signals/{id}`
 
@@ -261,6 +266,7 @@ erDiagram
         text name
         text keywords "JSON array"
         text description "NULL: none"
+        text icon "solid/robot, NULL: initials"
         bigint created
     }
     signal_verdicts {
@@ -272,8 +278,12 @@ erDiagram
 ```
 
 - `signals` and `signal_verdicts` are created from their entities like every table
-  (`crates/ipx/src/entity.rs`). `users.typesafe_key` and `signals.description` were added to
-  existing tables, so `create_missing` adds each column when it is missing.
+  (`crates/ipx/src/entity.rs`). `users.typesafe_key`, `signals.description` and `signals.icon`
+  were added to existing tables, so `create_missing` adds each column when it is missing.
+- The icons are files of ipx-web's, not the database's: `web/build.mjs` copies Font Awesome Free's
+  SVGs to `/icons/<style>/<name>.svg`, kept a day, and writes `/icons/index.json`, names, labels
+  and search terms, about 90 KB compressed, named by its hash and fetched when the picker first
+  opens. A Signal's tile draws its one file as a CSS mask, so it takes the theme's colour.
 - A Signal's list is `entries_where` with
   `EXISTS (SELECT 1 FROM signal_verdicts v WHERE v.signal_id = $n AND v.feed_id = e.feed_id AND v.guid = e.guid AND v.hit)`
   on top of the subscribed-feeds scope. So filters, search, sort, block lists and read state all