CodeMorph gets its own identity

Every trace of stock branding removed, Copilot removed, and a visual identity built around Geist, Bricolage Grotesque and a warm dark theme.

Removed the built-in GitHub Copilot extension and its onboarding. Morph will be the built-in agent.
Removed all stock editor branding, with an automated guard in CI that fails the build if any slips back in.
Telemetry off: telemetry and crash-report endpoints are disabled in the product configuration.
Open VSX is the extension registry.
Corrected setting defaults so CodeMorph's chosen defaults actually apply on a fresh install.

Fonts: Geist for the interface, Geist Mono in the editor and Bricolage Grotesque for display type, all bundled and open source.
CodeMorph theme as the default: warm near-black surfaces with an orange accent.
Floating panels: borderless cards with consistent gaps and corner radii, a reworked tab strip, status bar and scrollbars.
The CodeMorph drop in the title bar and as the empty-editor watermark, checksummed in CI so it can't be altered by accident.
The empty editor lists the main actions: Start Migration, Run & Verify, New Agent Chat, Open Folder, Show Terminal and Search Files.