Allow provider reordering in tray panel

[Finesssee]

Summary

Adds provider display ordering as shared settings state and wires it through Settings, tray panel, pop-out, dense tray slots, native tray bridge, and backend provider snapshots. Also adds reliable accessible Move up / Move down controls for provider rows while keeping drag/drop and keyboard reorder behavior.

Adds contributor issue/PR templates and CONTRIBUTING guidance for future UI visual proof with CUA Driver and pre-submit thermo-nuclear code quality review.

Closes #90

Affected areas

• Tray panel
• Settings UI
• Config file / settings persistence
• CLI
• Provider-specific behavior
• Installer / release packaging
• Startup / background behavior
• Documentation
• Other:

Validation

• cargo test --manifest-path rust\Cargo.toml
• cargo test --manifest-path apps\desktop-tauri\src-tauri\Cargo.toml
• cargo fmt --all
• cargo clippy --manifest-path rust\Cargo.toml --all-targets -- -D warnings
• cargo clippy --manifest-path apps\desktop-tauri\src-tauri\Cargo.toml --all-targets -- -D warnings
• pnpm --dir apps\desktop-tauri test
• pnpm --dir apps\desktop-tauri run build
• Thermo-nuclear code quality review completed before submitting: https://github.com/cursor/plugins/blob/main/cursor-team-kit/skills/thermo-nuclear-code-quality-review/SKILL.md
• Focused regression checks: backend partial config order tests and src\lib\providerOrder.test.ts

UI / tray proof

• Not applicable
• CUA Driver visual proof attached
• CUA Driver could not be used; equivalent manual proof and explanation attached

CUA Driver verified config-file order Gemini -> Claude -> Codex in Settings and tray panel, and verified the Settings Move up / Move down controls persist order into the tray panel.

Notes for reviewers

Provider order is canonicalized in shared Rust settings and then consumed by bridge/catalog/tray/frontend surfaces to avoid per-surface ordering drift.