feat: add session config sidebar with override level, tools, and permissions

Implements issue #13 — right sidebar for session configuration with
override level selection, disabled tools checkboxes, and granted
permissions input. Integrates config into chat page header with toggle
button and non-default indicator.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

implementation-plans/issue-013.md

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+---
+---
+
+# Issue #13: Session config sidebar component
+
+**Status:** COMPLETED
+**Issue:** https://git.shahondin1624.de/llm-multiverse/llm-multiverse-ui/issues/13
+**Branch:** `feature/issue-13-config-sidebar`
+
+## Acceptance Criteria
+
+- [x] Right sidebar component for session configuration
+- [x] Override level selection (None / Relax / All) with radio-style buttons
+- [x] Disabled tools toggle checkboxes using ToolType enum values
+- [x] Granted permissions free-text input with add/remove
+- [x] Toggle button in header with non-default config indicator dot
+- [x] Reset button to restore defaults
+- [x] Config passed to processRequest on send
+
+## Implementation
+
+### Components
+- `ConfigSidebar.svelte` — right sidebar with override level, disabled tools, and granted permissions sections
+- Updated `+page.svelte` — added config toggle button in header, sessionConfig state, and ConfigSidebar integration
+
+### Key Decisions
+- Used `@bufbuild/protobuf` `create()` with `SessionConfigSchema` for immutable config updates
+- Config state lives in `+page.svelte` and is passed down as prop
+- Non-default config indicator (amber dot) shown in both the header toggle button and sidebar header
+- Disabled tools stored as string labels matching ToolType enum display names