Plugin vendor crates lack any translation support (~300+ hardcoded English strings)

Summary

All 6 plugin vendor crates have zero translation support — no rust-i18n dependency, no t!() calls, no locale files. Collectively they contain ~300+ hardcoded English UI strings that cannot be localized.

This was previously tracked in #63 ("We need a way for plugin UI to support localization") which was closed, but the underlying gap remains.

Affected crates and estimated hardcoded strings

Crate	Est. Strings	Key examples
blueprint_editor	~100+	Toolbar (Save, Compile, Debug), palette search, properties panel, overlay zoom/debug, prefab/event/macro panels
shader_editor	~50+	Toolbar (Save, Compile, Reload), panel titles, palette, properties, compilation messages, overlay zoom
matter_editor	~25+	Toolbar (Paint, Eraser, Fill, Eyedropper), layers panel, color panel, properties
code_editor	~25+	Toolbar (New File, Save, Find, Run), file explorer, status bar (Ln/Col, encoding), welcome screen
asset_viewer	~20+	Properties sections (File, Info, Transform, View), mesh stats, viewport labels
table_editor	~30+	Query editor toolbar (Execute, Clear, Export CSV/JSON), row actions (Add, Duplicate, Delete)

Common patterns

All crates hardcode strings via these patterns:

• .child("English text") — text nodes
• .tooltip("English text") — button tooltips
• .label("English text") — button labels
• .placeholder("English text") — input placeholders
• .title(...) returning "English text" — panel titles
• format!("English text {}", value) — dynamic strings (zoom %, counts, etc.)
• PluginMetadata / FileTypeDefinition fields — plugin names, descriptions, categories

Additionally, "Editor not available" is a shared fallback string duplicated across multiple plugins.

Suggested approach

1. Establish a plugin i18n pattern — either each plugin crate vendors its own locales/ + rust_i18n::i18n!(), or a shared mechanism via a plugin SDK crate
2. Add rust-i18n dependency to each plugin crate's Cargo.toml
3. Create locales/en.yml for each crate with all keys
4. Replace all hardcoded strings with t!("Key.Name") calls
5. Add locale files for other supported languages