Add a Sinatra server that keeps boards in SQLite

Nullboard's storage layer bottoms out in getItem/setItem/delItem over
string keys, with boards, revisions and undo history all modelled on top
of them client-side. So the server needs to be nothing more than a
key/value store, and it doesn't parse a board anywhere.

One password, bcrypt-hashed, in the same database as the boards. The
session secret lives there too, so restarting the service doesn't sign
you out and the secret never has to exist in the unit file or in git.

Until a password is set every route returns 503 pointing at
bin/validboard-passwd. A first-run setup page would be friendlier, but it
would also hand the board to whoever found the URL first.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UU1vyTHj3uE9PJYSxRxwkU

README.nullboard.md

@@ -0,0 +1,132 @@
+# Nullboard
+
+Nullboard is a minimalist take on a kanban board / a task list manager, designed to be compact, readable and quick in use.
+
+https://nullboard.io/preview
+
+![Nullboard](images/nullboard-example-alt.png)
+
+The name also happens to abbreviate to [NB](https://en.wikipedia.org/wiki/Nota_bene), which I think is a nice touch.
+
+## Dead simple
+
+* Single-page web app - just one HTML file, an ancient jQuery package and a webfont pack.
+* Can be used completely offline. In fact, it's written exactly with this use in mind.
+
+## Locally stored
+
+* All data is stored locally, for now using [localStorage](https://developer.mozilla.org/en/docs/Web/API/Window/localStorage).
+* The data can be exported to- or imported from a plain text file in a simple JSON format.
+* The data can also be automatically backed up to a local disk with the help of:
+  * [Nullboard Agent](https://nullboard.io/backups) - a native Windows app
+  * [Nullboard Agent Express Port](https://github.com/justinpchang/nullboard-agent-express) - an express.js-based portable app
+  * [nbagent](https://github.com/luismedel/nbagent) - a version for Unix systems, in Python
+
+## Beta
+
+Still very much in beta. Caveat emptor and all that.
+
+## UI & UX
+
+The whole thing is largely about making it convenient to use.
+
+Everything is editable in place, all changes are saved automatically and last 50 revisions are kept for undo/redo:
+
+![In-place editing](images/nullboard-inplace-editing.gif)
+
+New notes can be quickly added directly where they are needed, e.g. before or after existing notes:
+
+![Ctrl-add note](images/nullboard-ctrl-add-note.gif)
+
+Notes can also be dragged around, including to and from other lists:
+
+![Drag-n-drop](images/nullboard-drag-n-drop.gif)
+
+Nearly all controls are hidden by default to reduce visual clutter to its minimum:
+
+![Hidden controls](images/nullboard-hidden-controls.gif)
+
+Longer notes can be collapsed to show just the first line, for even more compact view of the board:
+
+![Collapsed notes](images/nullboard-collapsed-notes.gif)
+
+The default font is [Barlow](https://tribby.com/fonts/barlow/) - it's both narrow *and* still very legible. Absolutely fantastic design!
+
+![Barlow speciment](images/barlow-specimen.png)
+
+Notes can also be set to look a bit different. This is useful for partitioning lists into sections:
+
+![Raw notes](images/nullboard-raw-notes.gif)
+
+Links starting with https:// and http:// are recognized. They will "pulse" on mouse hover and can be opened via the right-click menu.
+
+![Links on hover](images/nullboard-links-on-hover.gif)
+
+Pressing CapsLock will highlight all links and make them left-clickable.
+
+![Links reveal](images/nullboard-links-reveal.gif)
+
+Lists can be moved around as well, though not as flashy as notes:
+
+![List swapping](images/nullboard-list-swap.gif)
+
+The font can be changed; its size and line height can be adjusted:
+
+![Theme and zoom](images/nullboard-ui-preferences.gif)
+
+The color theme can be inverted:
+
+![Dark theme](images/nullboard-dark-theme.gif)
+
+Also:
+
+* Support for multiple boards with near-instant switching
+* Undo/redo for 50 revisions per board (configurable in the code)
+* Keyboard shortcuts, including Tab'ing through notes
+
+## Caveats
+
+* Written for desktop and keyboard/mouse use
+* Essentially untested on mobile devices and against tap/touch input
+* Works in Firefox, tested in Chrome, should work in Safari and may work in Edge (or what it's called now)
+* Uses localStorage for storing boards/lists/notes, so be careful around [clearing your cache](https://stackoverflow.com/questions/9948284/how-persistent-is-localstorage)
+
+You spot a bug, file an issue.
+
+## Dockerized version
+
+See [this fork](https://github.com/rsoper/nullboard).
+
+## Background
+
+Nullboard is something that handles ToDo lists in the way that works really well. For *me* that is.
+
+Tried a lot of options, some were almost *it*, but none was 100%.
+
+**Trello** wasn't bad, but never was comfortable with the idea of storing my data in cloud without any actual need.
+
+**Wekan** looked promising, but ultimately too heavy and had no offline usage support or a local storage option.
+
+**Things** was beautiful, but not the right tool for the job.
+
+**Inkscape** - I kid you not - with a laundry list of text items was actually OK, but didn't scale well.
+
+Ditto for the plain **text files**.
+
+Pieces of **paper** were almost there, but rearranging items can be quite a hassle.
+
+So finally got annoyed enough to sit down and write exactly what I wanted.
+
+And, voilà, Nullboard came out  =>  https://nullboard.io/preview
+
+## License
+
+The [2-clause BSD license](https://opensource.org/licenses/BSD-2-Clause/) with the [Commons Clause](https://commonsclause.com/).
+
+That is, you can use, change and re-distribute it for as long as you don't try and sell it.
+
+## Updates
+
+Primary feed is through [@nullboard](https://twitter.com/nullboard) on Twitter.
+
+The changelog is here => https://nullboard.io/changes