feat: add --quota flag to rtk gain with tier-based analysis

Implements heuristic calculation of monthly quota savings percentage
with support for Pro, Max 5x, and Max 20x subscription tiers.

Features:
- --quota flag displays monthly quota analysis
- --tier <pro|5x|20x> selects subscription tier (default: 20x)
- Heuristic based on ~44K tokens/5h Pro baseline
- Estimates: Pro=6M, 5x=30M, 20x=120M tokens/month
- Clear disclaimer about rolling 5-hour windows vs monthly caps

Example output for Max 20x:
  Subscription tier:        Max 20x ($200/mo)
  Estimated monthly quota:  120.0M
  Tokens saved (lifetime):  356.7K
  Quota preserved:          0.3%

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: FlorianBruniaux

src/gain.rs

@@ -1,7 +1,7 @@
 use anyhow::Result;
 use crate::tracking::Tracker;
 
-pub fn run(graph: bool, history: bool, verbose: u8) -> Result<()> {
+pub fn run(graph: bool, history: bool, quota: bool, tier: &str, _verbose: u8) -> Result<()> {
     let tracker = Tracker::new()?;
     let summary = tracker.get_summary()?;
 
@@ -68,6 +68,29 @@ pub fn run(graph: bool, history: bool, verbose: u8) -> Result<()> {
         }
     }
 
+    if quota {
+        const ESTIMATED_PRO_MONTHLY: usize = 6_000_000; // ~6M tokens/month (heuristic: ~44K/5h × 6 periods/day × 30 days)
+
+        let (quota_tokens, tier_name) = match tier {
+            "pro" => (ESTIMATED_PRO_MONTHLY, "Pro ($20/mo)"),
+            "5x" => (ESTIMATED_PRO_MONTHLY * 5, "Max 5x ($100/mo)"),
+            "20x" => (ESTIMATED_PRO_MONTHLY * 20, "Max 20x ($200/mo)"),
+            _ => (ESTIMATED_PRO_MONTHLY, "Pro ($20/mo)"), // default fallback
+        };
+
+        let quota_pct = (summary.total_saved as f64 / quota_tokens as f64) * 100.0;
+
+        println!("Monthly Quota Analysis:");
+        println!("────────────────────────────────────────");
+        println!("Subscription tier:        {}", tier_name);
+        println!("Estimated monthly quota:  {}", format_tokens(quota_tokens));
+        println!("Tokens saved (lifetime):  {}", format_tokens(summary.total_saved));
+        println!("Quota preserved:          {:.1}%", quota_pct);
+        println!();
+        println!("Note: Heuristic estimate based on ~44K tokens/5h (Pro baseline)");
+        println!("      Actual limits use rolling 5-hour windows, not monthly caps.");
+    }
+
     Ok(())
 }
 

src/main.rs

@@ -232,6 +232,12 @@ enum Commands {
         /// Show recent command history
         #[arg(short = 'H', long)]
         history: bool,
+        /// Show monthly quota savings estimate
+        #[arg(short, long)]
+        quota: bool,
+        /// Subscription tier for quota calculation: pro, 5x, 20x
+        #[arg(short, long, default_value = "20x", requires = "quota")]
+        tier: String,
     },
 
     /// Show or create configuration file
@@ -519,8 +525,8 @@ fn main() -> Result<()> {
             }
         }
 
-        Commands::Gain { graph, history } => {
-            gain::run(graph, history, cli.verbose)?;
+        Commands::Gain { graph, history, quota, tier } => {
+            gain::run(graph, history, quota, &tier, cli.verbose)?;
         }
 
         Commands::Config { create } => {