docs: add SetupService to architecture, update changelog and testing docs

- ARCHITECTURE.md: add setup_service.py to services list
- CHANGELOG.md: add Unreleased section with folder scan key resolution fix
- TESTING.md: add SetupService testing section with example tests

docs/CHANGELOG.md

@@ -37,6 +37,17 @@ This changelog follows [Keep a Changelog](https://keepachangelog.com/) principle
 
 ---
 
+## [Unreleased] - 2026-06-05
+
+### Fixed
+
+- **Folder scan series key resolution**: Fixed "Could not resolve series key for folder, skipping" warnings during library setup. `_resolve_key_via_search()` now uses fuzzy title matching instead of exact string comparison.
+    - Added `_normalize_title()` to strip anime suffixes: `(TV)`, `(Anime)`, `(OAD)`, `(OVA)`, `(Special)`, `(Movie)`, `(Spin-Off)`
+    - Added `_titles_match()` using `difflib.SequenceMatcher` with 0.85 similarity threshold for tolerance of minor title variations
+    - Added debug logging for title mismatches and multiple search results
+
+---
+
 ## [1.3.1] - 2026-02-22
 
 ### Added