Add secure/password mode for canvas text fields

Problem

Canvas <text-field> has no password/secure-input mode. Apps that accept API keys or tokens must either render plaintext or keep a second masked buffer whose value intentionally diverges from the editor model.

That workaround can break normal caret/selection/IME reconciliation and cannot provide native protected-text accessibility semantics.

Requested API

A markup/API flag such as:

<text-field secure=true text={secret} on-input=secret_edit />

Expected behavior:

• render a mask instead of the value;
• expose protected/password semantics through accessibility bridges;
• redact the value from automation snapshots, journals, diagnostics, and clipboard copy/cut;
• keep paste and normal TextInputEvent editing functional;
• never serialize the plaintext as display-list text.

Current application workaround

Applications currently need to maintain a separate masked buffer whose value diverges from the editor model. This is limited, can break caret/selection/IME reconciliation, and cannot provide protected accessibility semantics.

Native SDK 0.6.3 on Windows 11.

Start by locating the canvas implementation and its TextInputEvent, accessibility, automation, journal, diagnostics, clipboard, and display-list paths. Define the secure=true behavior against the requested API and verify that masking, protected accessibility semantics, functional editing, redaction, and plaintext exclusion all work together.