docs(user): dashboard, browsing, profile rewrites + new podcasts guide; trash stubs

Ground-truthed against the templates this pass:
- dashboard.md: real section kinds (system shelves incl. Continue
  Series, user collections, custom sections via /custom-section
  builder), Customize Dashboard panel semantics (per-library, drag,
  switches, 10-50 items, Save Changes), Refresh, This Week widget,
  per-item Read/Listen and progress-conflict resolve actions. The old
  page listed a wrong shelf set and never mentioned custom sections.
- library-browsing.md: the file was secretly titled 'Saving Custom
  Filters' and covered nothing else. Now the browsing page: All Books
  toolbar (search, Sort, Filters -> drawer hand-off, Save/Load/Clear
  saved filters), book detail as hub, series pages, podcasts split.
- profile-guide.md: field table ground-truthed from profile_form.templ
  (username/email DO remain editable there), audio defaults (speed,
  resume rewind, keep awake), timezone rendering contract, both theme
  doors (7-pick select vs 37-theme Appearance panel), Change Password
  with live checks, Danger Zone/Remove My Account + last-admin rule.
- podcasts.md NEW: the Podcasts page had zero documentation. Subscribing
  (Add Feed -> RSS URL, library, back-catalog download, download order,
  Add & Subscribe), Continue/All Feeds, Download All, player + Play as
  Sequence cross-link.
- Trashed user-areas.md, frontend-guide.md, settings-guide.md: stubs
  whose planned content now exists as real pages (or duplicates
  profile-guide). user-guide.md rewritten as the plain-language front
  door with a go-here-when table; index.md rows updated to match.
- ui-controls.md: 10 new gate-checked entries for every newly cited
  control (Add & Subscribe via templ-entity fragment).

docs/user/podcasts.md

@@ -0,0 +1,47 @@
+# Podcasts
+
+Bookhoard is not just books: it also runs your podcast subscriptions. You
+subscribe to feeds, episodes download for offline listening, and you can
+play a run of episodes back-to-back — a feed, or a hand-picked sequence.
+
+## The Podcasts page
+
+Open **Podcasts** from the sidebar. The page is your subscriptions:
+
+- **Continue** — the episode you were in the middle of, ready to resume
+- **All Feeds** — every feed you subscribe to
+- **Search** narrows your feeds and episodes
+- Each feed's page holds its episodes, with **Download All** for grabbing
+  everything at once
+
+Subscriptions live in your **Podcasts library** (feeds manage it themselves —
+you won't see it in the regular library switcher, and it never mixes into
+the book wall on **All Books**).
+
+## Subscribing to a feed
+
+1. Click **Add Feed** on the Podcasts page
+2. In the **Add Podcast Feed** panel, paste the show's **RSS feed URL**
+3. Choose the **Library** the podcast belongs to
+4. Optionally: check **Download all episodes now** to grab the back catalog
+   immediately, and pick the **Download order** for new episodes — **Feed
+   order**, **Feed order (reversed)**, **Oldest first (pub date)**, or
+   **Newest first (pub date)**
+5. Click **Add & Subscribe**
+
+From then on Bookhoard watches the feed: new episodes appear as the show
+publishes them, downloaded according to the order you picked.
+
+## Playing episodes
+
+Click an episode to open the audio player. The player keeps your place,
+supports bookmarks, a chapter list where the show provides chapters, and
+playback speed — the same speed and resume-rewind defaults you set on your
+[profile](profile-guide.md) apply here.
+
+To play many episodes in a row, use a collection: episode collections have a
+**Play as Sequence** button and their own listening order — see
+[Collections](collections.md).
+
+*Finding your way back:* **Podcasts** is the sidebar page whose header reads
+"Your subscriptions" — the only page with the **Add Feed** button.