Correct docs and the sort label ahead of the next release

[callicles]

Pre-release docs and consistency cleanup, from a QA + documentation audit of main ahead of cutting 0.5.0. No behavior changes except one user-visible label.

What changed

CHANGELOG.md

• The TTL-outlier entry now links issue TTL advisory reports the max across resolvers, so one outlier reports 2h23m for a 300s zone #35 alongside PR Stop one resolver's invented TTL from setting the TTL advisory #38, matching every sibling entry's style.
• The 80-column entry now mentions the Time → Ping header rename and that --once prints the same name/location/IP widths and right-aligns its TTL — both shipped in Fit the table in 80 columns, badge errors, coarsen the countdown #40 but were undocumented, and the --once format is documented as script-consumable.
• The error-badge entry now names the third badged element (the not a domain name label), not just the status glyph and word.
• Removed a stray blank line inside 0.4.0's Added section (formatting only).

README.md

• Nix pin example bumped v0.3.1 → v0.4.0 (newest existing tag).
• Ctrl+S sort list says ping instead of time, matching the label change below.

src/app.rs — SortMode::label returns "ping" instead of "time", so the footer's sort: … agrees with the column header #40 renamed. Covered by the amended #40 changelog entry per the AGENTS.md amendment rule (behavior introduced in [Unreleased]).

src/main.rs — the long --help's [theme] block documents the "<fg> on <bg>" badge form added in #40:

# error = "white on lightred"  # "<fg> on <bg>" badges the failure marker

AGENTS.md — module map brought up to date: sites.rs is NSID-first with id.server as fallback (#39); added the missing theme.rs, globe.rs, and world_data.rs rows; config.rs owns theme/ecs/view as well as resolvers; app.rs also owns the table column layout (#40's TableLayout).

Verification

cargo fmt --check                         → clean
cargo clippy --all-targets -- -D warnings → clean
cargo test                                → 120 passed; 0 failed

cargo run -- example.com --once smoke-tested. PTY run of the real binary confirms the footer now cycles sort: resolver → location → ping → status → answer, agreeing with the README table and the Ping column header. --help shows the new theme line at the width of the surrounding block.

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