docs: delete four documents that contradict the code

They do not merely lag it, they contradict it, which is worse than
absent: the only way to find out one is wrong is to trust it.

docs/dev/roadmap.md, 1648 lines. Its "Current State" describes an app
with basic playback, a track list and an album grid. Phases 1, 2, 3 and
5 have shipped entire -- playlists, shuffle and repeat, shortcuts,
virtualised lists, search, custom columns, smart playlists, the
MusicBrainz client, autotag. Its Decision Log records "Testing:
Deferred" against 836 Vitest tests, a Playwright suite on two engines
and race-detector passes in three build configurations.

.pi/journal.md, "what happened and what's next", frozen at plan 005 and
still saying everything from phase 1 onward is uncommitted. That is the
tracker's job now, and a work log that is wrong about what is committed
is a hazard rather than a stale file.

docs/dev/overview.md, a shallower and partly incorrect CLAUDE.md
architecture section. README pointed at it and points at CLAUDE.md now.

docs/dev/config-suggestions.md, eight suggestions of which one survived
-- the rest were overtaken by rewrites: applyDefaults exists, scan
concurrency is configurable with SSD/HDD detection, and httphandler.go
and the WriteHeader-after-render bug it described are gone entirely.

Nothing is lost: the genuinely unbuilt work was filed first, as #94
device sync, #95 layout customisation, #96 AcoustID and #97 the config
setters that take no lock.

Refs #98

README.md

@@ -106,5 +106,8 @@ make dev          # run with hot-reload
 make build-prod   # produce a release binary
 ```
 
-More detail for contributors lives in
-[`docs/dev/overview.md`](./docs/dev/overview.md) and [`CLAUDE.md`](./CLAUDE.md).
+More detail for contributors lives in [`CLAUDE.md`](./CLAUDE.md) — the
+architecture, the conventions and the reasons behind them. What is
+being worked on is [the issue
+tracker](https://git.ljones.me/yonlu/yellowjacket/issues); #73 is the
+roadmap.