Add Sonarr client and series search/add flow (M3)

Sonarr client with lookup, add series (monitor modes) and search.
Refactor the movie view into a generic search view driven by a backend
interface so Movies and Series share one implementation.
Add F1-F4 / Alt+1-4 view switching that works while typing.

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:** M2 done
+- **Status:** M3 done
 
 ## 1. Goals
 
@@ -101,6 +101,7 @@ Keybindings (initial proposal):
 | Key | Action |
 |---|---|
 | `Tab` / `1-4` | Switch view |
+| `F1-F4` / `Alt+1-4` | Switch view, also while typing in a search box |
 | `/` | Focus search |
 | `Enter` | Search / open details / confirm |
 | `a` | Add selected result |
@@ -183,7 +184,7 @@ The file should be created with mode `0600`; warn if it is more permissive. API
 - [x] **M0** — Project skeleton: `go mod init`, config loading, empty tview app with tabs and status bar.
 - [x] **M1** — Radarr client: system status, lookup, quality profiles, root folders, add movie.
 - [x] **M2** — Movie search + add flow in the UI.
-- [ ] **M3** — Sonarr client and series search + add flow.
+- [x] **M3** — Sonarr client and series search + add flow.
 - [ ] **M4** — SABnzbd client and Downloads view (queue + history) with live updates and pause/resume/delete.
 - [ ] **M5** — Radarr/Sonarr queues merged into the Downloads view.
 - [ ] **M6** — Interactive release search (movies, then series seasons/episodes) and grab.