Land v0.4.0 pre-release source content: docs, changelog, packaging

Bring the source tree to its finished v0.4.0 content state ahead of the
release candidate. Documentation, changelog, release notes, and
packaging metadata only; no code or version-string changes.

CHANGELOG.md: backfill the operator-visible changes that landed since
v0.3.0 (the show_metrics scraper query and fipsctl stats metrics, the
discovery dedup-cache-full counter, the off-rx_loop control read
surface and its new daemon-resolved fields, the fipstop TUI overhaul,
the TCP inbound cap now honoring max_connections, host-map hot-reload,
log-noise demotions, and the net bug fixes), topic-grouped rather than
replayed per commit; intra-cycle fixes folded into their feature
entries; the duplicate Unreleased Fixed section merged into one.

Release notes: author docs/releases/release-notes-v0.4.0.md to the
operator-upgrade bar and mirror it byte-for-byte into the root
RELEASE-NOTES.md. Attribute each feature to its author in Contributors
(Nym transport and the mixnet demo to @oleksky, opt-in mDNS LAN
discovery to @mmalmi).

README.md: add the Nym transport to the support matrix (Linux, macOS,
Windows; OpenWrt pending verification), the multi-transport bullet, and
the "What works today" list; fold mDNS LAN discovery into the existing
Nostr-discovery bullets; refresh the status narrative to v0.4.0 over a
global, public test mesh.

packaging/common/fips.yaml: add commented Nym transport and mDNS LAN
discovery example stanzas with verified field names and defaults.

Cargo.toml: add homepage, keywords, and categories crate metadata.

docs/reference: update the cli-fips version example to the released
form; document the new control-socket output fields and the typed
RejectReason families in control-socket.md; sync cli-fipstop.md with the
overhauled TUI keybindings.

Cargo.toml

@@ -6,7 +6,10 @@ description = "A distributed, decentralized network routing protocol for mesh no
 license = "MIT"
 authors = ["Johnathan Corgan <jcorgan@corganlabs.com>"]
 repository = "https://github.com/jmcorgan/fips"
+homepage = "https://fips.network"
 readme = "README.md"
+keywords = ["mesh", "p2p", "decentralized", "overlay-network", "nostr"]
+categories = ["network-programming", "command-line-utilities", "cryptography"]
 
 [dependencies]
 ratatui = "0.30"