Replace Hitster references with Music Cards branding

Updated all references from "Hitster-style" to generic "Music Cards"
throughout the codebase and documentation. This removes brand-specific
terminology and provides a more neutral description of the tool's purpose.

🤖 Generated with [Claude Code](https://claude.ai/code)

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

CLAUDE.md

@@ -1,12 +1,12 @@
 # Guide for this repository
 
 ## Project overview
-- Goal: Generate printable DIN A4 sheets with ‘Hitster-style’ music cards from a Spotify playlist. Front shows a QR code plus the title and artist(s); back shows the release year and small text.
+- Goal: Generate printable DIN A4 sheets with music cards from a Spotify playlist. Front shows a QR code plus the title and artist(s); back shows the release year and small text.
 - Current core: generate_hitster_cards.py uses Spotify’s Web API, generates QR codes and PDF pages with 3 × 3 cards per A4 (each 63 × 88 millimetres).
 - Outputs:
   - Separate files mode: fronts.pdf and backs.pdf.
   - Interleaved mode: cards.pdf with alternating pages (odd fronts, even backs) via --one-pdf.
-- Scope: Personal, non-commercial use; not affiliated with Hitster or Spotify.
+- Scope: Personal, non-commercial use; not affiliated with Spotify.
 
 ## Key requirements and constraints
 - Paper and layout:
@@ -61,7 +61,7 @@
 - Avoid copying full API payloads to logs; redact where necessary.
 
 ## Known limitations and non-goals
-- The Hitster iPhone app will not scan these QR codes; they are standard QR codes to open.spotify.com, not Hitster’s proprietary format.
+- These are standard QR codes that link to open.spotify.com for universal compatibility with any QR code scanner.
 - Album.release_date year may differ from an original single’s first release in some catalogues.
 - Client credentials flow cannot read private playlists; that requires user login (authorisation code flow).
 
@@ -110,4 +110,4 @@
 
 ## Licence and attribution
 - Use for personal, non-commercial purposes only.
-- Not affiliated with or endorsed by Hitster or Spotify.
+- Not affiliated with or endorsed by Spotify.