TUI: Context panel help text isn't tab-aware (Owners/Auth show repo labels)

[DanielCardonaRojas]

Context

Raised by CodeRabbit on #225.

In crates/codemark-tui/src/browser/bindings.rs, the FocusArea::ContextPanel branch of get_help_bindings (and the status-bar get_context_bindings) pushes repository-oriented labels unconditionally:

FocusArea::ContextPanel => {
    bindings.push(("Enter", "Select repo"));
    bindings.push(("Space", "Toggle repo"));
    ...
}

The Context panel has three tabs (Repos, Owners, Auth), but the help text always describes repo actions regardless of the active ContextTab:

• Owners tab — Enter/Space toggle the selected owner (filtering the repo list), so "Select repo"/"Toggle repo" is misleading.
• Auth tab — read-only; neither key activates anything, yet the bindings still advertise repo actions.

This is a pre-existing inaccuracy (the labels previously read "Toggle repo"/"Toggle repo"); #225 only reworded the Repos-tab case.

Proposal

Branch the Enter/Space help labels by the active ContextTab:

• Repos: Enter → Select repo, Space → Toggle repo
• Owners: Enter/Space → Toggle owner
• Auth: omit the Enter/Space repo bindings

Keep unrelated bindings (resize, etc.) unchanged. Apply the same treatment to the status-bar bindings.

Severity

Minor / UX polish. No functional impact.