feat: Claude Code CLI v2.1.105–v2.1.131 support (#274)

## Overview

Full audit and implementation of Claude Code CLI changelog entries from v2.1.105 through v2.1.131.

## Changes

### Implemented

- **#268** — Add `claude-opus-4-7` to the model picker, update all model pricing and context window sizes (also fixes a bug where `claude-opus-4-6` was coded as 200K context instead of 1M)
- **#269** — Expose effort level setting in UI via `--effort <level>` flag (`low`, `medium`, `high`, `xhigh`, `max`)
- **#273** — Expose prompt caching TTL env vars in UI (`ENABLE_PROMPT_CACHING_1H` / `FORCE_PROMPT_CACHING_5M`)
- **#267** — Add `PreCompact` hook support — emits `claude:pre-compact` event with "Compacting context..." toast and thinking state
- **#270** — Parse `plugin_errors` from stream-json init event and surface them as error output lines
- **#266** — Bump supported CLI version constant to `2.1.131`

### Closed as Not Applicable

- **#271** (`autoScrollEnabled`) — TUI-only setting; we manage our own scroll behaviour
- **#272** (`tui` fullscreen mode) — TUI-only setting; we use stream-json and never activate the TUI

## Testing

All checks pass (`./check-all.sh`) including frontend lint, format, type check, Vitest coverage, Clippy, and Rust test coverage.

✨ This PR was created with help from Hikari~ 🌸

Reviewed-on: #274
Co-authored-by: Hikari <hikari@nhcarrigan.com>
Co-committed-by: Hikari <hikari@nhcarrigan.com>

src/lib/components/UserQuestionModal.svelte

@@ -118,6 +118,8 @@
           bare_mode: config.bare_mode ?? false,
           show_clear_context_on_plan_accept: config.show_clear_context_on_plan_accept ?? true,
           custom_model_option: config.custom_model_option || null,
+          effort_level: config.effort_level || null,
+          prompt_caching_ttl: config.prompt_caching_ttl || null,
         },
       });