Editor context bridge: send selections, diagnostics, and diffs into CodeWhale

[Hmbown]

Problem

IDE-first users expect an assistant to understand the file/range/diagnostic they are looking at. CodeWhale should support that job without becoming a full IDE fork. The terminal/TUI should remain the source of truth, while editors can hand it precise context.

Scope

For v0.8.47, design and implement the first editor-context bridge around ordinary CodeWhale sessions.

• Start with VS Code as the common denominator for classrooms and contributors.
• Support sending selected files/ranges, current diagnostics, and git diffs into the active CodeWhale session.
• Prefer protocol bridges such as ACP, MCP, or the local runtime API before creating a large first-party IDE surface.
• Keep the terminal/TUI session as the canonical session record.
• Do not attempt full inline code completion until workspace-indexing and latency are strong enough.
• Keep auth and runtime-token handling explicit.

Acceptance criteria

• A VS Code user can send current editor context to CodeWhale without copy/paste.
• The receiving CodeWhale session shows what context was added and from where.
• The bridge does not silently expose the runtime API beyond localhost/private configuration.
• Docs explain the difference between editor context handoff and a full IDE plugin.

Related: #1264, #1584, #1801
Related tracker: #1881