Fix three stale references found auditing today's own changes

[oroderico]

Documentation and a self-test comment had drifted from the code they describe. None of these are from today's PRs — the oldest predates them by a week — but all three surfaced while checking today's work for the same failure mode, and none had been caught since.

README's Controls section quoted footer text that no longer exists

L/R move BOTH select, BOTH continue L/R back and BOTH extend L/R erase — the board's two buttons sit one above the other, not side by side, and the code has said Up/Down since 5e23ce2 (8 Aug). That commit updated NAV_FOOTER, the timeout warning and the About screen's own prose, but never the top-level README describing the same buttons.

Worse than a wrong word: BOTH continue L/R back doesn't name any real footer any more. That screen moved to the chrome's tick, which draws no bar at all.

A self-test comment claimed a copy that no longer exists

dice_screen_hints_clear_the_bar said it tested "every hint the app actually shows, copied from collect_entropy()" — but all three hints, including the "Looks good - generate?" it quoted, migrated to nav_dice_confirm (83b7e46, 15 Aug) and are no longer passed to the plain renderer this test drives.

The check itself stayed valid despite that: seedtool_render_screen's two-line layout and seedtool_render_nav_text's share the same y=39/65 — which is exactly what nav_chrome_bands_do_not_collide's own comment leans on when it skips re-proving the 90..103 band. Fixed the hint text to match what nav_dice_confirm shows today, and the comment to explain why checking it through the plain renderer is still meaningful, rather than claiming a copy that no longer exists.

The audit skill pointed at a revoked ceiling and one contributor's machine

.claude/skills/audit/SKILL.md told an auditor to check the binary against a 295 KiB ceiling; tools/audit_origo_elf.py's default is 512 KiB, raised weeks ago and explained in that file's own comment. Read literally, today's 303920-byte build would score as over the limit instead of at 58% of it.

The skill also named one contributor's home directory and asserted their default IDF had drifted to 6.0.2 — a fact about a specific machine, stated as if it held everywhere. Replaced with placeholders and a pointer to dependencies.lock's pinned version, so the skill stops being accurate for exactly one filesystem.

Left alone

README's "Going back" section still describes a Back row at the end of every menu, which the chrome's arrow replaced weeks before this. Bigger than a wording fix — it needs rewriting for the current model, and possibly "Lists and scrolling" beside it — so it is flagged here rather than folded into this diff.

Verification

Host self-test and the 52 Python tests. No firmware change; nothing here touches main/ or the ELF.