[Feature Request] Add option to disable or customize context low warning banner

Bug Description
Issue:
The "context low" warning banner (e.g., "8% left - Run /compact to compact and continue")
is very intrusive. It takes up significant screen real estate and repeatedly interrupts
workflow, especially during longer sessions where context naturally depletes.

Current behavior:

• Large warning banner appears when context is low
• No way to dismiss or disable it
• Keeps appearing even after acknowledged

Requested feature:
Add a setting to control context warnings, similar to DISABLE_COST_WARNINGS. Options could
include:

{
"contextWarnings": "none" | "subtle" | "default"
}

Or environment variable:
DISABLE_CONTEXT_WARNINGS=1

Why this matters:

• Power users already monitor context via custom statusline
• The warning is redundant for users who are aware of context limits
• Screen space is valuable, especially on laptops
• Repeated warnings are distracting during focused work

Suggested alternatives to current banner:

• Single-line status message instead of large banner
• One-time notification per session (dismissible)
• Integrate with statusline API so users can handle it themselves

Environment Info

• Platform: darwin
• Terminal: iTerm.app
• Version: 2.0.72
• Feedback ID: 88435605-b862-49ce-aaef-9147d1cf9b62