feat: add Herdr terminal jump support

[lchojnowski]

Summary

• add Herdr as the first terminal-jump backend for same-session panes, tabs, and workspaces
• verify the selected PID through the Herdr pane process inventory before focusing
• recover stale inherited pane IDs from the live agent list without importing Herdr status into abtop

Safety and compatibility

• use direct argv calls to the documented Herdr 0.7.0+ CLI; no shell, dependency, setup, or network call
• pin every call to the current abtop HERDR_SOCKET_PATH and require an exact PID match
• parse only pane IDs and PIDs; do not retain titles, argv, or other Herdr metadata
• preserve existing jump eligibility and fallback behavior for cmux, tmux, and iTerm2

Herdr references: CLI reference and agent guide.

Testing

• rustfmt +1.88.0 --edition 2021 --check src/jump/herdr.rs src/jump/mod.rs src/app.rs
• cargo clippy --all-targets -- -D warnings
• cargo test --all-targets (210 passed)
• cargo build --release
• cargo check --target x86_64-unknown-linux-gnu
• cargo check --target x86_64-pc-windows-gnu
• git diff --check
• live Herdr 0.7.5 test: selected a live Claude session from abtop in a temporary pane; Enter focused its exact pane across workspaces, and --exit-on-jump returned the source pane to its shell after success

[lchojnowski]

@graykode, this is ready for review. It adds the requested Herdr terminal-jump backend, includes exact-PID and fail-closed coverage, and has been verified end to end against Herdr 0.7.5 across workspaces.

[lchojnowski]

A consolidated draft successor is now available at #166. It includes this Herdr branch, #163, and the subsequent Codex lifecycle, Herdr, CodexBar, privacy, and reliability work. I’m leaving this PR open until the maintainer decides how to review or replace the earlier branches.