feat: add native Oh My Pi provider support

[Devin-Pi]

Summary

• add native Oh My Pi (omp) app support across CLI, TUI, provider, prompt, session, usage, and configuration workflows
• manage OMP providers and models in the native models.yml format
• add OMP model roles, model discovery/fetch, prompt files, session scanning, and usage/token/cost statistics
• preserve OMP-native YAML fields and protect against overwriting external edits

Related issue

• Related to 能否支持 pi && omp #358: support Pi and Oh My Pi (OMP)

Issue #358 tracked the request for Pi and OMP support. Pi was later merged separately in #431; this PR implements the remaining OMP scope with native OMP configuration semantics rather than reusing the Pi adapter.

Scope

• adds first-class AppType::Omp routing instead of reusing the Pi adapter
• supports PI_CODING_AGENT_DIR, PI_CONFIG_DIR, OMP profiles, project/global role configuration, and native OMP path resolution
• supports provider/model CRUD while preserving multiple providers in models.yml
• switching the default model updates config.yml model roles; it does not delete or replace other providers
• adds --app omp model and role commands and an OMP TUI surface aligned with the existing app menus
• includes secure managed-directory checks, provider/model schema validation, unknown-field preservation, and revision/conflict detection

Compatibility

Existing Claude, Codex, Gemini, OpenCode, Hermes, OpenClaw, and Pi workflows remain unchanged. OMP configuration is kept separate from Pi configuration and uses OMP-native YAML files and environment variables.

Validation

• cargo fmt --all -- --check
• cargo check
• cargo test --lib -- --test-threads=1
• cargo test --bin cc-switch -- --test-threads=1
• cargo build --release
• git diff --check

Tests that touch OMP paths use isolated temporary directories and do not modify the host OMP, Claude, Codex, or CC-Switch configuration directories.