[Feature]: Add mechanical quick fixes for XAML diagnostics

Is your feature request related to a problem? Please describe.

The XAML language server detects the battle-test matrix accurately (33/33 in PR #50 Round 5), but only 9/18 scenarios expose a code action. Several diagnostics already contain enough structured information for a deterministic repair, leaving users to make routine edits manually.

Describe the solution you'd like

Add focused code actions for:

• missing namespace declarations (CA05): insert the required xmlns on the document root when the namespace is uniquely known;
• missing x:DataType (CA09): insert an inferred authoritative type when available;
• missing or invalid x:Name (CA11/CA16): generate a unique valid identifier;
• duplicate attributes (CA17): remove the duplicate attribute safely;
• unresolved namespace declarations (WXAML0033): offer a replacement only when a single close known namespace is authoritative.

Each action should preserve formatting, avoid guesses when multiple candidates exist, and include unit plus live integration coverage.

Additional context

Follow-up from PR #50 Round 5 battle testing. Detection is now the strong part of the feature; remediation is the largest remaining usability gap.

Start by reviewing the PR #50 Round 5 battle-testing context and the existing XAML language-server diagnostics for CA05, CA09, CA11, CA16, CA17, and WXAML0033. Implement focused actions only where the repair is deterministic, preserving formatting and avoiding ambiguous candidates. Add unit and live integration coverage for each supported action.