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.

src/config.rs

@@ -311,6 +311,42 @@ impl Config {
     }
 }
 
+#[cfg(test)]
+impl Config {
+    /// A configuration with nothing switched on, for tests.
+    pub fn for_tests(session_days: i64) -> Self {
+        Self {
+            username: "narl".into(),
+            password: "hunter2".into(),
+            secret: b"a-secret-of-at-least-16-bytes".to_vec(),
+            bind: "127.0.0.1:0".parse().unwrap(),
+            data_dir: ".".into(),
+            session_days,
+            max_upload_bytes: 1,
+            secure_cookie: false,
+            vault_idle: std::time::Duration::from_secs(60),
+            backup: BackupConfig {
+                device_name: "narl-diary".into(),
+                interval: None,
+                debounce: std::time::Duration::from_secs(0),
+                prune: false,
+                session_key_file: None,
+            },
+            mail: MailConfig {
+                url: None,
+                from: String::new(),
+                to: String::new(),
+                timezone: chrono_tz::UTC,
+                reminder_at: None,
+                card_due_at: None,
+                digest_at: None,
+                kinds: Vec::new(),
+            },
+            sftp: SftpConfig { bind: None },
+        }
+    }
+}
+
 impl MailConfig {
     fn from_env() -> Result<Self> {
         let url = var("SMTP_URL");