Replace token-usage panel with per-pane context-fill indicator

For a subscription user, lifetime token totals + a $ estimate aren't
actionable; how full each session's context window is right now is. So:

- Removed the UsagePanel, the titlebar 💰 chip, and Ctrl+Shift+U.
- Repurposed the transcript reader (src-tauri/src/usage.rs): get_pane_context
  returns each recent session's CURRENT context occupancy = the last
  assistant turn's input + cache_read + cache_creation tokens (the prompt
  size), instead of lifetime sums. Same UNC/$HOME/cache/recency machinery.
- src/lib/usage.ts now holds context helpers (window inference 200k vs 1M by
  whether occupancy already exceeds 200k, % , green→amber→red ramp, label).
- App polls get_pane_context (15s, visibility-gated) into a cwd→context map
  exposed via orchestration; each LeafPane looks itself up by leaf.cwd and
  renders a slim fill bar + % in its header (hidden for non-claude/unmatched
  panes).

Also fixes the narrow-pane toolbar: a ResizeObserver sets leaf--narrow /
leaf--xnarrow width tiers; the label shrinks first, split buttons / status /
secondary chips drop out by tier, and the close × + context indicator stay
pinned right and visible down to the 180px min width.

tsc clean (apart from the not-yet-installed xterm addons). Rust builds on
the Windows host; needs runtime verification.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/ipc.ts

@@ -39,33 +39,25 @@ export interface SshHost {
 
 export const listDistros = (): Promise<string[]> => invoke("list_distros");
 
-// ---- claude usage tracking ------------------------------------------------
+// ---- claude context tracking ----------------------------------------------
 
-/** Per-model token tally within one claude session. Mirrors Rust ModelUsage. */
-export interface ModelUsage {
-  model: string;
-  inputTokens: number;
-  outputTokens: number;
-  cacheCreationTokens: number;
-  cacheReadTokens: number;
-}
-
-/** One claude session's usage, read from its transcript. Mirrors Rust
- *  SessionUsage. Cost is computed frontend-side (see src/lib/usage.ts). */
-export interface SessionUsage {
+/** One claude session's current context-window occupancy, read from its
+ *  transcript. Mirrors Rust SessionContext. `contextTokens` is the prompt
+ *  size of the last assistant turn (input + both cache buckets). */
+export interface SessionContext {
   sessionId: string;
   cwd: string;
-  projectDir: string;
   distro: string;
   lastActiveMs: number;
-  models: ModelUsage[];
+  contextTokens: number;
+  model: string;
 }
 
-/** Scan ~/.claude/projects in the given WSL distros (distinct distros of
- *  open WSL panes) and return recent sessions' token tallies. WSL/Windows
- *  only — returns [] otherwise. */
-export const getClaudeUsage = (distros: string[]): Promise<SessionUsage[]> =>
-  invoke("get_claude_usage", { distros });
+/** Scan ~/.claude/projects in the given WSL distros (distinct distros of open
+ *  WSL panes) and return each recent session's current context occupancy.
+ *  WSL/Windows only — returns [] otherwise. */
+export const getPaneContext = (distros: string[]): Promise<SessionContext[]> =>
+  invoke("get_pane_context", { distros });
 
 export const spawnPane = (args: {
   spec: SpawnSpec;