Doc comments on ipx-feed's and ipx-directory's public items (#354)

The style guide asks for doc comments on a library's public API. Every
type, function, constant and static the two libraries export now has
one, saying what it is for or what it does that its name does not:
fetch follows redirects itself so credentials stay on the feed's host,
Config::parse refuses repeated token names, Store::due_one is the
admin's Refresh. Fields and variants whose names say it all have none,
as the guide allows.

category_path's comment had slid above categories(), which then had
two; each has its own again.

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

crates/directory/src/config.rs

@@ -6,9 +6,11 @@ use anyhow::{Context, Result, bail};
 use serde::Deserialize;
 use std::path::Path;
 
+/// `directory.toml`. See docs/directory.md.
 #[derive(Debug, Clone, Deserialize)]
 #[serde(deny_unknown_fields)]
 pub struct Config {
+    /// Where the API and the public pages listen.
     #[serde(default = "default_bind")]
     pub bind: String,
     /// The environment variable holding the database URL, so the file holds no secret.
@@ -39,6 +41,7 @@ fn default_database_url_env() -> String {
     "DIRECTORY_DATABASE_URL".into()
 }
 
+/// A token as `directory.toml` lists it: a name, what it may do, and only the token's hash.
 #[derive(Debug, Clone, Deserialize)]
 #[serde(deny_unknown_fields)]
 pub struct TokenCfg {
@@ -74,11 +77,14 @@ pub struct Token {
 }
 
 impl Config {
+    /// Reads and checks `path`; see `parse`.
     pub fn load(path: &Path) -> Result<Self> {
         let text = std::fs::read_to_string(path).with_context(|| format!("reading {}", path.display()))?;
         Self::parse(&text).with_context(|| format!("in {}", path.display()))
     }
 
+    /// Reads a config, refusing tokens with empty or repeated names, which would file two
+    /// instances' snapshots together.
     pub fn parse(text: &str) -> Result<Self> {
         let cfg: Config = toml::from_str(text)?;
         let mut seen = std::collections::HashSet::new();