docs: README in the standard order; setup files say what works today (#6277)

README: logo header, short summary, a compose quick start with one-line
comments, first-run steps, a configuration table, setup pitfalls,
updating and backups, then features grouped by what you do. The Specs
section (it called the Android client the "Flutter companion app"), the
dated tag-history sentence and the Fable pointer are gone. Feature lines
were checked against the code: radio seeds from a track only, and the
Android app plays from its cache rather than offering downloads.

.env.example used the SMARTMUSIC_ prefix, which the config loader has not
read for a long time, so copying it set nothing. It now uses MINSTREL_.

config.example.yaml is also the config the image bakes in at
/etc/smartmusic/config.yaml. It listed five recommendation weights
(base_weight, like_boost, recency_weight, skip_penalty, jitter_magnitude)
that moved to Admin > Tuning; yaml.Unmarshal ignored them silently. They
are removed, and the file parses to exactly Default(), so the running
server is unchanged. coverart_from_mbcaa is not listed: nothing reads it.

docker-compose.yml, the Makefile and the spec banners lose their task and
milestone ids.

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

docs/smart-music-client-spec.md

@@ -1,6 +1,6 @@
 # Project Spec: Smart Music Client (companion app)
 
-> **History.** This is the original design spec, kept as written. Where it describes an outside library manager doing search, adds and deletes, Minstrel now does that itself (M502).
+> **History.** This is the original design spec, kept as written. Where it describes an outside library manager doing search, adds and deletes, Minstrel now does that itself.
 
 ## 1. Overview
 

docs/smart-music-server-spec.md

@@ -1,6 +1,6 @@
 # Project Spec: Smart Music Server (working name)
 
-> **History.** This is the original design spec, kept as written. Where it describes an outside library manager doing search, adds and deletes, Minstrel now does that itself (M502).
+> **History.** This is the original design spec, kept as written. Where it describes an outside library manager doing search, adds and deletes, Minstrel now does that itself.
 
 ## 1. Overview