Open the 0.5.x maintenance line at 0.5.1-dev

The maintenance branch moves from the retired 0.4.x line to v0.5.0 and opens
for patch work. The move is a fast-forward, so no history is discarded, and
the old tip stays reachable through its own v0.4.2 tag.

The version becomes 0.5.1-dev and the changelog gets an empty Unreleased
heading, replacing the note that pointed at where the release content had
been folded. The status badge stays at v0.5.0: on this branch it names the
released version rather than the one in development, which is what it did
throughout the 0.4.x line.

CHANGELOG.md

@@ -7,9 +7,6 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
-Nothing yet. Everything previously staged here is folded into
-`[0.5.0]` below.
-
 ## [0.5.0] - 2026-08-30
 
 ### Added

Cargo.lock

@@ -1144,7 +1144,7 @@ checksum = "9844ddc3a6e533d62bba727eb6c28b5d360921d5175e9ff0f1e621a5c590a4d5"
 
 [[package]]
 name = "fips"
-version = "0.5.0"
+version = "0.5.1-dev"
 dependencies = [
  "arc-swap",
  "bech32 0.12.0",

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "fips"
-version = "0.5.0"
+version = "0.5.1-dev"
 edition = "2024"
 description = "A distributed, decentralized network routing protocol for mesh nodes connecting over arbitrary transports"
 license = "MIT"