v0.3.4 — Match the OpenPencil editor theme

The canvas toolbar, selection strip, loading wrapper, buttons, inputs and dialogs now match the Rust OpenPencil editor's neutral light/dark surfaces and blue accent. The compact 32 px selection strip remains unchanged.

Validated against the real Rust/WASM editor in the existing Chrome profile, including light/dark host switching, the optional prompt input, Save As, and an actual edit/save/reopen. Package checks, all 69 regression tests, and the installed plugin's bundled Codex host check passed (186 tools).

Reconnect the plugin and reopen the canvas after updating to load the new styling.