Add interactive release search (M6)

Release listing and grab in the shared arr client, a full-screen release
list (sort, hide rejected, rejection reasons, confirmation before grabbing
rejected releases; Usenet only), and a season/episode picker for Sonarr.
Overlays are now a stack so dialogs can open above the release list.
Add a fake Newznab indexer to the dev setup.

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

SPECS.md

@@ -6,7 +6,7 @@ A terminal UI to search for movies and series, add them to Radarr / Sonarr, and
 - **TUI library:** [tview](https://github.com/rivo/tview) (on top of tcell)
 - **License:** MIT
 - **Module:** `git.stinnesbeck.com/nils/arr-tui`
-- **Status:** M5 done
+- **Status:** M6 done
 
 ## 1. Goals
 
@@ -111,8 +111,10 @@ Keybindings (initial proposal):
 | `t` | Retry the selected failed download (history) |
 | `h` | Downloads view: cycle focus between SABnzbd queue, Radarr/Sonarr queue and history |
 | `b` | Downloads view (Radarr/Sonarr queue): blocklist the release and search for another |
-| `i` | Interactive release search for the selected item |
-| `g` | Grab the selected release |
+| `i` | Interactive release search for the selected library item (movies; series ask for a season, then an episode or the whole season) |
+| `g` / `Enter` | Release list: grab the selected release (rejected ones ask for confirmation) |
+| `s` / `f` | Release list: cycle sort (best / size / age) / hide rejected |
+| `Esc` | Close a dialog or the release list |
 | `r` | Refresh |
 | `?` | Help |
 | `q` / `Ctrl+C` | Quit |
@@ -190,7 +192,7 @@ The file should be created with mode `0600`; warn if it is more permissive. API
 - [x] **M3** — Sonarr client and series search + add flow.
 - [x] **M4** — SABnzbd client and Downloads view (queue + history) with live updates and pause/resume/delete.
 - [x] **M5** — Radarr/Sonarr queues merged into the Downloads view.
-- [ ] **M6** — Interactive release search (movies, then series seasons/episodes) and grab.
+- [x] **M6** — Interactive release search (movies, then series seasons/episodes) and grab.
 - [ ] **M7** — Polish: help screen, error handling, README, release builds.
 - [ ] **M8+** — v0.2 features (library view, series drill-down).