Stabilize termscp for 1.0.0

[veeso]

Summary

• stabilize core error handling by removing production panic/unwrap paths and normalizing localhost path handling
• split oversized auth/parser modules into focused submodules and add core/module API documentation
• add targeted regression coverage for parser, config, explorer, localhost, bookmarks, auto-update, and ssh key storage paths
• enable a safe clippy pedantic subset and fix the resulting low-risk diagnostics while keeping cargo clippy --no-default-features -- -Dwarnings green

Verification

• cargo +nightly fmt --all
• cargo build --no-default-features
• cargo clippy --no-default-features -- -Dwarnings
• targeted test runs for parser, config::serialization, explorer::formatter, host::localhost, and system::sshkey_storage modules

Notes

• the known flaky network probe test system::auto_update::test::test_should_check_whether_github_api_is_reachable still fails in restricted environments and was not used as a merge gate
• the original pedantic plan item was reduced to the lints that were safe on the current tree; needless_pass_by_value and semicolon_if_nothing_returned were intentionally not enabled because they exploded into broad UI refactors rather than a safe stabilization pass

[cocogitto-bot]

✔️ 43f2f8f...65f24c1 - Conventional commits check succeeded.