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/app/harness.rs

@@ -122,6 +122,7 @@ impl Harness {
     /// as risky because their behaviour is unknown.
     ///
     /// Return: `Verdict::Allow` or `Verdict::Block(reason)`.
+    #[allow(clippy::too_many_lines, clippy::unnecessary_debug_formatting)]
     pub fn gate_tool_call(
         tool_name: &str,
         args: &serde_json::Value,
@@ -163,8 +164,7 @@ impl Harness {
                 let allowed = workspace_roots.iter().any(|r| out_path.starts_with(r));
                 if !allowed {
                     return Verdict::Block(format!(
-                        "output path '{:?}' is outside all workspace roots",
-                        out_path
+                        "output path '{out_path:?}' is outside all workspace roots"
                     ));
                 }
             }
@@ -286,7 +286,7 @@ impl Harness {
                          (>= {MIN_REASON_LEN} chars) explaining why it is needed"
                     ));
                 }
-            } else if args.as_object().map(|m| !m.is_empty()).unwrap_or(false) {
+            } else if args.as_object().is_some_and(|m| !m.is_empty()) {
                 // Only require reason when there are meaningful arguments
                 return Verdict::Block(format!(
                     "MCP tool '{tool_name}' requires a 'reason' argument \