refactor(core): share discovery item ID prefixes

[IgorArkhipov]

Summary

• Move discovery-item ID prefixes into a shared ids module used by both inventory construction and toggle parsing.
• Remove duplicated Claude/Pi/OpenCode prefix literals that previously lived in both discovery.rs and mutation.rs.

Test Plan

• cargo fmt --all -- --check
• cargo clippy -p unpin-core --all-targets --all-features --locked -- -D warnings
• cargo test -p unpin-core --all-features --locked --lib
• cargo test -p unpin-core --all-features --locked --test discovery --test mutation --test provider_registry
• cargo clippy --workspace --all-targets --all-features --locked -- -D warnings
• cargo test --workspace --all-features --locked
• cargo run -p unpin-cli --locked -- --help
• cargo audit --deny warnings
• cargo machete
• Pi/OpenCode disposable-root host validation when release-impacting
• Full local provider matrix run and finalized when release-impacting

Safety Checklist

• Tests and examples do not read real home-directory provider state.
• Tests and examples do not use .env* files.
• Write paths use dry-run planning, confirmation, backup, audit, and restore behavior where relevant.
• Provider changes stay within the current Claude Code, Codex CLI, Cursor,
  Pi, OpenCode, and Zed support scope.
• Public docs or examples were updated when user-facing behavior changed.

Reviewer Notes

No behavior change. Compat skill namespaces and Cursor marketplace settings keys stay in discovery; this only consolidates item ID prefixes. Independent of #57.

Not a release candidate; provider matrix and live-host validation were not run.

Made with Cursor