Dialectic URL parser doesn't handle spaces in regex patterns

[nikomatsakis]

Problem

Dialectic URLs with spaces in regex patterns fail to parse correctly. The Rust MCP server should automatically URL-encode spaces to %20 but currently doesn't.

Example

This walkthrough contains a broken dialectic URL:

# Action Button Code Flow Walkthrough

Let's trace what happens when you click an action button in the walkthrough system.

**Current Status**: Buttons render but clicking fails due to CSP violations and missing message handlers.

## Current Implementation

These links should now work properly:

**Step 1**: Button HTML generation in [renderSection](dialectic:extension/src/walkthroughWebview.ts?regex=onclick.*handleAction)

**Step 2**: JavaScript handleAction function in [webview script](dialectic:extension/src/walkthroughWebview.ts?regex=function handleAction)

**Step 3**: Message sent to extension via [vscode.postMessage](dialectic:extension/src/walkthroughWebview.ts?regex=vscode.postMessage)

**Step 4**: Extension receives message in [handleWebviewMessage](dialectic:extension/src/walkthroughWebview.ts?regex=handleWebviewMessage)

## The Problem

**CSP Issue**: Inline `onclick` handlers violate Content Security Policy
**Missing Handler**: Extension doesn't handle `'action'` message type  
**No IPC**: No communication back to MCP server/AI assistant

Broken URL

dialectic:extension/src/walkthroughWebview.ts?regex=function handleAction

The space in function handleAction causes the URL parsing to fail.

Working Workaround

dialectic:extension/src/walkthroughWebview.ts?regex=function.*handleAction

Using .* instead of a space works.

Expected Behavior

The Rust dialectic URL processor should:

1. Automatically URL-encode spaces in regex patterns (function handleAction → function%20handleAction)
2. Parse URLs with spaces correctly
3. Give clear error messages when URL parsing fails

Current Behavior

URLs with spaces in regex patterns silently fail - no navigation occurs and no error is shown.

Impact

This affects the usability of walkthrough system when trying to search for multi-word patterns in code.