feat(honeybar): the HoneyOS bar, loaded at runtime

A strip along the top that leads to the other apps of the same system. It is
served by HoneyOS; InkNote only says where to find it, through
INKNOTE_HONEYBAR_ORIGIN. Empty means no bar and no change at all.

The origin is served by the API rather than built into the page, because an
image is pulled ready-made and a service worker keeps whole responses: anything
frozen into index.html would outlive the setting.

Layout follows the bar through --honeybar-h. The body has overflow:hidden, so
the surplus height would not have scrolled but been cut off at the bottom; and
#root padded itself around the notch that the bar now covers, which would have
counted that gap twice.

Unit 263/263, all fourteen browser suites green.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

readme.md

@@ -169,6 +169,26 @@ The web UI listens on port `3000`, the API only inside the compose network. If a
 reverse proxy sits in front, bind the port to localhost (`"127.0.0.1:3000:80"`),
 otherwise the app is reachable on the host's address without TLS.
 
+#### The HoneyOS bar
+
+`INKNOTE_HONEYBAR_ORIGIN` puts a strip along the top of every page that leads to
+the other apps of the same system — it is served by HoneyOS, so what it looks
+like and which apps it lists are settled there, not here. Empty means no bar at
+all, and nothing about the app changes.
+
+The value takes effect on restart: the page asks the server for it
+(`GET /api/public/config`) and loads the script itself. It is deliberately not
+built into the image — an image is pulled ready-made, and a service worker keeps
+whole responses, so anything frozen into `index.html` would outlive the setting.
+
+`INKNOTE_HONEYBAR_KEY` is only needed when HoneyOS sits on a *different site*
+than InkNote (`honeyos.example.com` vs `notes.example.org`). The browser then
+withholds the HoneyOS session, and the bar has no other way to ask for the list
+of apps. Under a shared domain it can stay empty.
+
+Offline there is no bar — it comes from another server. The app itself is
+unaffected, which is the right way round for one that is built to work offline.
+
 ---
 
 ## API Reference