chore(release): move to independent per-crate versioning at 0.5.0

Each workspace crate now owns its own version instead of the previous
lockstep scheme; irtt-proto, irtt-client, irtt-server, irtt-stats, and
irtt-cli all become 0.5.0 as the first independently-versioned release.
Workspace dependency requirements are bumped to match.

Add a root CHANGELOG.md with a real per-crate 0.5.0 section drawn from
archaeology of every merge since v0.4.0, not just path-filtered commits.

Move cargo-dist to a crate-qualified `irtt-cli/vX.Y.Z` tag namespace so
only irtt-cli (the one dist-able application) triggers a GitHub Release;
library crate tags (irtt-proto/irtt-client/irtt-server/irtt-stats) exist
purely to pin the source for a crates.io release and no longer risk
tripping the release workflow. Regenerate the renamed
irtt-cli-release.yml via `dist generate` and update the few other files
that referenced the old release.yml path by name. Also fix a stale
`features = ["full"]` in dist-workspace.toml left over from a feature-flag
refactor that dropped the "full" feature entirely, which was silently
breaking every dist build.

Rescope semver.yml's tag trigger to the same five crate-qualified tags
so semver checks keep running under the new convention.

dist-workspace.toml

@@ -11,5 +11,7 @@ ci = "github"
 installers = []
 # Target platforms to build apps for (Rust target-triple syntax)
 targets = ["aarch64-apple-darwin", "aarch64-unknown-linux-gnu", "x86_64-apple-darwin", "x86_64-unknown-linux-gnu", "x86_64-unknown-linux-musl", "x86_64-pc-windows-msvc"]
-# Features to pass to cargo build
-features = ["full"]
+# Scope dist's tag matching to irtt-cli releases only: irtt-proto/irtt-client/
+# irtt-server/irtt-stats are libraries published to crates.io and tagged for
+# provenance, but must not trigger cargo-dist or produce a GitHub Release.
+tag-namespace = "irtt-cli"