chore(release): 0.31.0, mark as fork build

Bump 0.29.0 -> 0.31.0 (three feature milestones past upstream 0.28) and
tag every build with "-fork" in build.rs, so `gitui --version` and the
help popup read e.g. "0.31.0-fork <date> (<hash>)" and never look like
an upstream release. Restamp the changelog heading to [0.31.0].

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LrbVApNVj46mmVyzfqgDsx

Author: stevenpollack

CHANGELOG.md

@@ -7,7 +7,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## Unreleased
 
-## [0.29.0] - 2026-07-15
+## [0.31.0] - 2026-07-15
 
 ### Added
 * support x509 commit signing [[@kaden-l-nelson](https://github.com/kaden-l-nelson)] ([#2514](https://github.com/gitui-org/gitui/issues/2514))

Cargo.lock

@@ -1,6 +1,6 @@
 [package]
 name = "gitui"
-version = "0.29.0"
+version = "0.31.0"
 authors = ["extrawurst <mail@rusticorn.com>"]
 description = "blazing fast terminal-ui for git"
 edition = "2021"

Cargo.toml

@@ -33,11 +33,13 @@ fn main() {
 	};
 	let build_date = now.date_naive();
 
+	// this is a fork build — mark the version as such so `gitui
+	// --version` and the help popup never read as an upstream release.
 	let build_name = if std::env::var("GITUI_RELEASE").is_ok() {
-		env!("CARGO_PKG_VERSION").to_string()
+		format!("{}-fork", env!("CARGO_PKG_VERSION"))
 	} else {
 		format!(
-			"{}-nightly {} ({})",
+			"{}-fork {} ({})",
 			env!("CARGO_PKG_VERSION"),
 			build_date,
 			get_git_hash()