fix(tui): use actual tmux prefix in welcome dialog and status bar

[redhelix]

Description

AOE hardcodes Ctrl+b as the tmux prefix in two places:

• The first-run welcome dialog (src/tui/dialogs/welcome.rs)
• The session status bar injected into every agent session (src/tmux/status_bar.rs)

Users who configure a non-default tmux prefix (e.g. Ctrl+a, which is common) see misleading detach instructions. This fix reads the actual configured prefix at runtime via tmux show-option -gv prefix and displays it correctly.

Changes

• src/tmux/utils.rs: Added tmux_prefix_display() — reads tmux show-option -gv prefix, converts tmux notation (C-a, M-b) to human-readable form (Ctrl+a, Alt+b), falls back to Ctrl+b if tmux is unavailable.
• src/tmux/mod.rs: Re-exports tmux_prefix_display from the public API.
• src/tui/dialogs/welcome.rs: Welcome dialog now calls tmux_prefix_display() for all three prefix references (detach key, scroll key, and the note line).
• src/tmux/status_bar.rs: apply_status_bar() now calls tmux_prefix_display() so the status-left injected into each agent session shows the correct prefix.

Root cause

Reported by a user whose tmux prefix is C-a. The status bar displayed Ctrl+b d to detach; pressing Ctrl+b d did nothing; pressing the actual prefix Ctrl+a d worked. The mismatch caused confusion about whether AOE itself was broken.

PR Type

• New Feature
• Bug Fix
• Refactor
• Documentation
• Infrastructure / CI

Checklist

• I understand the code I am submitting
• New and existing tests pass
• Documentation was updated where necessary
• For UI changes: included screenshot or recording

Testing

• cargo test passes (existing test_enter_submits, test_esc_submits, test_space_submits, test_other_keys_continue in welcome.rs all green)
• Manually verified on a machine with prefix = C-a: welcome dialog shows Ctrl+a then d, status bar shows Ctrl+a d to detach
• Fallback tested: with tmux not on PATH, tmux_prefix_display() returns Ctrl+b

AI Usage

• AI was used for drafting/refactoring

AI Model/Tool used: Claude Sonnet 4.6 (Claude Code)

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