docs: retire the two root queues, archive the ranking (V-447)

PROGRESS.md and 20-07-2026-BACKLOG.md were state snapshots that git log and
the Vikunja board already carry. Everything PROGRESS.md claimed as shipped is
a QA task. The backlog's only untracked item, bounded follow-up state, is now
V-448.

maven-feature-ranking.md moves to docs/archive/2026-07-03-feature-ranking.md
instead of dying. Its mandatory and easy tiers became V-449 through V-458; the
doable and epic tiers are reasoning about why things are not worth doing yet,
which no task captures.

Four code comments and the design.md ledger pointed at the deleted files.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Xwomr2cT93KMSz9u3digX5

docs/design.md

@@ -672,8 +672,8 @@ Broadening to home automation, media or comms is JSON, not code.
 
 ## Execution ledger
 
-Condensed from `ROADMAP.md` (2026-07-06). The live queue is
-`20-07-2026-BACKLOG.md`; current state is `PROGRESS.md`.
+Condensed from `ROADMAP.md` (2026-07-06). The live queue is the Vikunja board
+(project Maven, ID 2); this table is history, not a work list.
 
 | # | Item | Prio | Status |
 |---|------|------|--------|