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>

Makefile

@@ -13,11 +13,8 @@ generate:
 generate-go:
 	go run github.com/sqlc-dev/sqlc/cmd/sqlc@v$(SQLC_VERSION) generate
 
-# Fail if the committed generated code no longer matches the .sql sources.
-#
-# Nothing verified this before, so internal/db/dbq could silently drift from
-# internal/db/queries — a hand-edit, a half-applied regen, or a schema change
-# without a regen would all pass CI while the typed layer lied about the SQL.
+# Fail if the committed generated code no longer matches the .sql sources:
+# a hand-edit, a half-applied regen, or a schema change without a regen.
 #
 # The diff is printed BEFORE the exit-code check on purpose: when this fails,
 # the log then contains sqlc's exact expected output, which is what you commit.
@@ -36,8 +33,8 @@ test-short:
 	go test -short -race ./...
 
 # Full suite incl. integration tests, against the dedicated minstrel_test
-# DB so a run never truncates the dev `minstrel` DB (Fable #339). Ensures
-# the test DB exists (idempotent — createdb errors if present, ignored).
+# DB so a run never truncates the dev `minstrel` DB. Ensures the test DB
+# exists (createdb fails harmlessly if it is already there).
 test-integration:
 	docker compose up -d postgres
 	-docker compose exec -T postgres createdb -U minstrel minstrel_test