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.

.gitignore

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+/target