ci: add GitHub Actions workflows with semantic-release auto-versioning

chore: fix all 702 clippy warnings across codebase
- auto-fix 475 via cargo clippy --fix
- fix remaining 227 manually: uninlined_format_args, redundant_closure, match_same_arms,
  underscore_binding, format_push_string, items_after_statements, needless_pass_by_value,
  clone_on_copy, case_sensitive_extension, single_match/let-else, write_with_newline,
  and other clippy lints

src/model/mod.rs

@@ -1,5 +1,5 @@
 //! Persistence and domain model layer: sessions, conversations, memory,
-//! message log (SQLite), edit log, and app/settings config.
+//! message log (`SQLite`), edit log, and app/settings config.
 
 pub mod app_config;
 pub mod editlog;