Schedule pickers, and target progress at one row

"Check feeds every" becomes a number plus a unit dropdown in both global
and per-feed settings; parse_interval gained weeks to back it. The
per-feed dropdown can select the global default, clearing the override.

Fixes progress painting every pending row: the event carried no enclosure
id, so the handler had nothing to target and set the width on all of them.
Adding a feed looked like it was downloading everything. Progress,
DownloadDone and DownloadError now carry the enclosure id.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AdXho5tTkjFLeUXKbEjKBh

src/db.rs

@@ -333,6 +333,7 @@ impl Db {
 /// An enclosure waiting to be downloaded.
 #[derive(Debug)]
 pub struct Pending {
+    pub id: i64,
     pub url: String,
     pub mime: Option<String>,
 }
@@ -343,12 +344,12 @@ impl Db {
     pub fn pending(&self, feed_id: &str, limit: usize) -> Result<Vec<Pending>> {
         let conn = self.conn.lock().unwrap();
         let mut stmt = conn.prepare(
-            "SELECT url, mime FROM enclosures
+            "SELECT id, url, mime FROM enclosures
              WHERE feed_id = ?1 AND state = 'pending' ORDER BY id LIMIT ?2",
         )?;
         let rows = stmt
             .query_map(rusqlite::params![feed_id, limit as i64], |r| {
-                Ok(Pending { url: r.get(0)?, mime: r.get(1)? })
+                Ok(Pending { id: r.get(0)?, url: r.get(1)?, mime: r.get(2)? })
             })?
             .collect::<rusqlite::Result<Vec<_>>>()?;
         Ok(rows)