docs, help, checks: the README and the help say what the app does

README: the API table lists every route, twelve of which were missing;
an SFTP section says how to turn the mount on and register a key; the
keys table and the command list cover what was only in the code
(digits, Tab, w, f, Alt-h/l, Ctrl-D/U, m/p, :today, :edit, :next and
the rest, :search!, :set clipboard, :logout!). Three claims that were
wrong are fixed: there is no board button above the list, R does not
rename a space, and Esc/q close the document.

Help gains the agenda keys and the board's gg/G and r. :t no longer
means :today, which read as the agenda's key.

make check runs cargo fmt --check, after the one formatting commit
before this, which .git-blame-ignore-revs names (git config
blame.ignoreRevsFile .git-blame-ignore-revs). Cargo.toml states
rust-version 1.96, the floor the Proton crates set, and the build is
checked on it. make build installs the frontend from the lockfile.

A test reads the route table out of routes/mod.rs and asks every route
without a cookie: all but the login, the health check and the share
links must answer 401, including any route added later.

web/src/lib/Help.svelte

@@ -41,6 +41,7 @@
     ['rule', 'the first list is the inbox, the last list is done'],
     ['h / l', 'to the list left / right'],
     ['j / k', 'down / up the cards'],
+    ['gg / G', 'first / last card of the list'],
     ['J / K', 'move the card down / up its list'],
     ['H / L', 'move the card to the list left / right'],
     ['Space', 'into the done list, or back out to the inbox'],
@@ -49,10 +50,19 @@
     ['D', 'due date: fri, tm, +3d, 10-31 …'],
     ['R', 'rename the card, or the list when it is empty'],
     ['z', 'show done cards older than a week'],
+    ['r', 'read the board again, for changes made elsewhere'],
     ['x · dd', 'delete the card (asks y/N)'],
     ['q · Esc', 'back to the tree'],
   ]
 
+  const agendaKeys: [string, string][] = [
+    ['j / k', 'down / up the cards'],
+    ['Enter', 'to the card, on its own board'],
+    ['Space', 'done, where it stands'],
+    ['T', "today's diary entry"],
+    ['t · q · Esc', 'close the agenda'],
+  ]
+
   const titles: Record<Group, string> = {
     tree: 'spaces & folders',
     board: 'boards',
@@ -99,6 +109,16 @@
       </dl>
     </section>
 
+    <section class="keys">
+      <h2>agenda keys</h2>
+      <dl>
+        {#each agendaKeys as [key, description] (key)}
+          <dt>{key}</dt>
+          <dd>{description}</dd>
+        {/each}
+      </dl>
+    </section>
+
     {#each grouped as [group, specs] (group)}
       <section>
         <h2>{titles[group]}</h2>