Replace cap-based estimation with PTY-driven 'claude /usage' parser

The widget now spawns 'claude' via portable-pty, sends /usage, parses the
three rendered bars (Current session / Current week all / Current week
Sonnet), and shows the real percentages in the ring + weekly bars. A
background task refreshes every 5 minutes; the title-bar refresh button
forces an immediate fetch.

Drops the cap-tuning UI and tier card from Settings; adds a 'claude command'
override (e.g. 'wsl.exe -- claude' for Windows-host widgets reading WSL
credentials) and a refresh-interval setting. Fixes title-bar buttons getting
swallowed as drag attempts via data-tauri-drag-region="false".

src-tauri/src/state.rs

@@ -5,6 +5,7 @@ use std::collections::{HashMap, HashSet};
 use std::path::PathBuf;
 use std::sync::Arc;
 
+use crate::cli_usage::CliUsage;
 use crate::jsonl::UsageEvent;
 use crate::settings::Settings;
 use crate::watch::WatcherHandle;
@@ -23,6 +24,9 @@ pub struct AppState {
     pub files: RwLock<HashMap<PathBuf, FileCache>>,
     pub seen_ids: RwLock<HashSet<String>>,
     pub settings: RwLock<Settings>,
+    /// Latest /usage result. Refreshed periodically by a background task,
+    /// or on-demand via the `refresh_cli_usage` command.
+    pub cli_usage: RwLock<Option<CliUsage>>,
     /// Boxed so we can keep the watcher alive across the whole app lifetime
     /// without polluting Tauri's setup hook.
     pub watcher: Mutex<Option<WatcherHandle>>,
@@ -37,6 +41,7 @@ impl AppState {
             files: RwLock::new(HashMap::new()),
             seen_ids: RwLock::new(HashSet::new()),
             settings: RwLock::new(settings),
+            cli_usage: RwLock::new(None),
             watcher: Mutex::new(None),
         })
     }