docs(admin): all-podcasts page — the maintenance view

Seventh admin page. Documents the disk-usage sort (hogs surface first),
the header totals, each column's meaning (orphaned = no subscribers,
usually a departed user's feed), and the three actions with their real
semantics: Refresh (manual poll vs. the Settings→Podcasts interval),
Delete files (resets episodes to pending, re-download on demand, and
the non-obvious part quoted: a refresh will not re-materialize them),
Remove (instance-wide: rows + files + everyone's subscriptions, unlike
a user's own unsubscribe). Cross-links the user podcast guide for the
listening side. Glossary gains Delete files and a scoped Remove.

docs/admin/podcasts.md

@@ -0,0 +1,51 @@
+<!-- Ground truth: templates/admin_podcasts.templ (table, actions, orphaned
+     badge, header totals, design comment: sorted by disk usage), internal/
+     router/frontend.go (/admin/podcasts handler), podcast polling/download
+     settings in internal/database/settings_registry.go (SettingsDefaults,
+     Podcasts group). Re-verify against these when the page changes. -->
+
+# All Podcasts
+
+This is the maintenance view for the podcast subsystem: **every feed from
+every user**, sorted by disk usage, so the biggest disk hogs surface
+first. (The listening side — subscribing, playing, downloading episodes —
+lives in the [user podcast guide](../user/podcasts.md); this page is
+about running the thing.)
+
+## The header totals
+
+Above the table: how many feeds exist, how many episodes are downloaded
+versus total, and how much disk the downloads occupy instance-wide.
+
+## The table
+
+One row per feed:
+
+| Column | Meaning |
+| --- | --- |
+| **Feed** | Title (links to its podcast page) and host |
+| **Library** | Which library holds it |
+| **Subscribers** | How many users subscribe (hover for names). **orphaned** means nobody does — usually a departed user's feed |
+| **Downloaded** | Episodes on disk / episodes the feed has published |
+| **Disk** | Space the downloaded files occupy |
+| **Last fetch** | When the feed was last checked for new episodes |
+
+## Actions, per feed
+
+- **Refresh** — checks the feed for new episodes right now, instead of
+  waiting for the automatic poll (its interval lives in Settings →
+  Podcasts).
+- **Delete files** (only when episodes are downloaded) — frees the disk
+  and resets those episodes to *pending*. They re-download on demand when
+  someone plays them. The confirm says the important part: **a feed
+  refresh will not re-materialize them** — deleting files is safe and
+  reversible by playback, not by refresh.
+- **Remove** — the admin delete: removes the feed, its episode rows, its
+  downloaded files, and everyone's subscriptions. This is instance-wide
+  (the confirm says so); a user removing their own subscription from the
+  listening side only affects that user.
+
+## When the page is empty
+
+"No podcast feeds exist yet." — feeds appear when users add them (or when
+you do, from the podcast section of the app).