Replace generated runner scripts with Rust

[wokalski]

Replace the generated shell control plane with one manifest-driven Rust crate while preserving real tmux PTYs.

• evaluate each shell into an immutable JSON manifest from Nix
• use clap derives for typed dnvr, logs, state, and completion arguments
• generate Bash, Zsh, Fish, and Nushell completions from the clap command tree
• move session creation, reattachment, pane lifecycle, PID locks, and stale-state cleanup into Rust
• ship a lightweight standalone dnvr-state binary without TUI dependencies
• keep shell execution only at intentional boundaries: user process commands, prerun, shell activation, and configured ref resolvers
• keep tmux-owned Rust recorder workers and independent raw/plain rotated logs
• remove the old generated Bash controller, Bash state program, Nushell logs frontend, completion templates, external flock calls, Python port picker, and dead generic runner scaffold
• preserve live sidebar upgrades and recorder replacement across reattachment

The live PTY pass found and fixed two integration bugs: macOS preserving the dnvr symlink identity for private worker commands, and trailing whitespace trimming dropping the last live pane's empty exit-status field. The latter now has a regression test.

Verified with Rust 1.86-compatible dependency resolution, rustfmt, strict Clippy across all targets/features, all Rust tests, full Nix builds of the specialized runner and minimal standalone state package, and a clean tmux PTY run covering all process rows, PID-lock status, raw/plain logs, Ctrl-G detach, reattach, and session cleanup.