[Chat] Display context window usage percentage indicator

Problem

During long development sessions, the conversation context window fills up silently until Claude suddenly loses track of earlier work, starts hallucinating file contents, or the session needs to be compacted/restarted. There is no visible indicator of how much context has been consumed, leaving developers blind to an approaching limit that directly impacts output quality.

Current Behavior

• No context usage information is displayed anywhere in the chat interface.
• Users only realize the context is running low when:
• Claude starts "forgetting" earlier instructions or file contents.
• A forced compaction occurs (which can lose nuanced context).
• The session abruptly ends or degrades in quality.
• This leads to wasted time: developers continue adding complex instructions not knowing the context is nearly full, resulting in poor outputs that need to be redone in a fresh session.

Expected Behavior

A context usage indicator visible in the chat area, showing:

• Percentage used: e.g., Context: 42% or a progress bar.
• Visual color coding:
• 🟢 Green (0–60%): Plenty of room, work freely.
• 🟡 Yellow (60–80%): Consider wrapping up complex tasks or compacting.
• 🔴 Red (80–100%): Critical — finish current task, prepare for new session.

Why This Matters

• Optimizes work pacing: Developers can plan when to compact, commit, or start fresh — instead of being surprised.
• Prevents quality degradation: Knowing the context is at 85% means the developer won't start a complex multi-file refactor that will fail halfway.
• Saves time and money: Avoidable redo-work caused by context overflow is a real productivity drain on professional workflows.
• Transparency builds trust: Users should know the state of the system they're interacting with — context capacity is a fundamental constraint that should be visible, not hidden.

Suggested Implementation

• A small, non-intrusive indicator near the chat input area (e.g., bottom-left corner or next to the model name).
• Format: 📊 Context: 42% or a thin progress bar.
• Tooltip on hover showing: ~420K / 1M tokens used.
• Optional: a setting to show/hide the indicator for users who don't want it.
• Color transitions at 60% and 80% thresholds.

Environment

• Claude Code Desktop App (Windows 11)
• Daily professional use with long development sessions (often hitting context limits)