Add .tmux.conf layout preset key bindings

[limijd]

Motivation

• Provide quick, repeatable workspace layouts for development and monitoring workflows via tmux key bindings.

Description

• Add a repository-level .tmux.conf that defines layout presets bound to prefix + 1/2/3/4/6/8, a zoom toggle on prefix + 9, and a grid auto-arrange helper on prefix + g.
• Implement pane creation for multi-pane presets using a POSIX-compatible while loop inside run-shell for better portability in /bin/sh contexts.
• Use tmux select-layout variants (even-horizontal, tiled) to normalize final pane arrangements.

Testing

• Verified the bundled tmux binary with ./tools/linux_x86_64/tmux/3.5a/tmux -V, which returned a valid version string.
• Loaded and sourced the new configuration using ./tools/linux_x86_64/tmux/3.5a/tmux -f .tmux.conf -L nvimprokit-test start-server \; source-file .tmux.conf \; kill-server, which completed without errors.

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[chatgpt-codex-connector]

Avoid shelling out to plain tmux in layout bindings

These presets run via run-shell and then invoke tmux by name, which fails when the server was started from a non-PATH binary (for example the vendored ./tools/.../tmux path) or on hosts without a global tmux install; in that setup the command returns 127 and the layout shortcut does nothing. Prefer native tmux command chaining for these bindings (or otherwise avoid relying on PATH resolution for tmux) so the presets work with the same binary that started the session.

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