[Feature Request] Allow configuring position of 'Context left until auto-compact' indicator in footer

Allow users to configure the position of the "Context left until auto-compact: X%" indicator within the footer layout.

Current Behavior

The auto-compact indicator is always rendered right-aligned on the first row of the statusline area:

[Opus 4.6] 📁 TRIPS | 🌿 master Context left until auto-compact: 7%
████░░░ 77% | $6.23 | 135m 20s | ↓6.8k ↑16.3k ⚡152.7k | +221 -0
▶▶ accept edits on (shift+tab to cycle)

Desired Behavior

Allow the indicator to be positioned below the permission mode bar (bottom row):

[Opus 4.6] 📁 TRIPS | 🌿 master
████░░░ 77% | $6.23 | 135m 20s | ↓6.8k ↑16.3k ⚡152.7k | +221 -0
▶▶ accept edits on (shift+tab to cycle)
Context left until auto-compact: 7%

Use Case

With a custom statusline that already displays context usage (progress bar + percentage), the right-aligned indicator on row 1 is redundant and clutters the layout. Moving it to the bottom row would:

• Free up horizontal space on the first row for custom content fully
• Putting it on the bottom row is less disruptive
• Give users more control over their footer layout

Related Issues

• #28710 — hide indicator entirely (subset of this)
• #27864 — layout squeeze on narrow terminals (alternative placement would help)
• #16151 (closed) — move entire statusline (different scope)