feat: initial implementation of jjf

A TUI revision picker for jujutsu (jj). Wraps any jj subcommand with an
inline fuzzy-finder over jj log, then forwards the picked revision(s)
as -r '<id>' to the underlying jj invocation.

Features:
- Inline viewport (no full-screen alt-screen takeover)
- Smart prefix matching: typing the bold portion of a change ID jumps
  to that revision instantly
- Multi-select via Tab; emitted as -r 'A|B|C' revset union
- Preflight detection of subcommands that don't accept -r
- Optional shell integration (jjf init <bash|zsh|fish|nu>) that
  rewrites shell history so up-arrow recalls the resolved jj command

Hand-rolled ANSI rendering to /dev/tty; only crossterm, nucleo-matcher,
anyhow, and libc as runtime dependencies.

src/init/zsh.sh

@@ -0,0 +1,25 @@
+jjf() {
+    # Meta-commands and bare flags bypass the picker and run the binary directly.
+    if [ $# -eq 0 ] || [ "$1" = "init" ] || [ "${1#-}" != "$1" ]; then
+        command jjf "$@"
+        return $?
+    fi
+    local _jjf_cmd
+    _jjf_cmd="$(command jjf --emit "$@")" || return $?
+    [ -n "$_jjf_cmd" ] || return 130
+    print -s -- "$_jjf_cmd"
+    sh -c "$_jjf_cmd"
+}
+
+# Suppress zsh from recording `jjf …` invocations; jjf appends the resolved
+# jj command itself via `print -s`.
+autoload -Uz add-zsh-hook 2>/dev/null
+_jjf_zshaddhistory() {
+    case "$1" in
+        jjf\ *|jjf$'\n'*) return 1 ;;
+    esac
+    return 0
+}
+if typeset -f add-zsh-hook >/dev/null; then
+    add-zsh-hook zshaddhistory _jjf_zshaddhistory
+fi