fix: resolve all clippy --all-targets warnings across 15 files

- gateway/mod.rs: move send_json before test module (items_after_test_module)
- memory/vector.rs: fix float_cmp, cast_precision_loss, approx_constant
- memory/chunker.rs: fix format_collect, format_push_string, write_with_newline
- memory/sqlite.rs: fix useless_vec
- heartbeat/engine.rs: fix format_collect, write_with_newline
- config/schema.rs: fix needless_raw_string_hashes
- tools/composio.rs: fix needless_raw_string_hashes
- integrations/registry.rs: fix uninlined_format_args, unused import
- tunnel/mod.rs: fix doc_markdown
- skills/mod.rs: allow similar_names in test module
- channels/cli.rs: fix unreadable_literal
- observability/mod.rs: fix manual_string_new
- runtime/mod.rs: fix manual_string_new
- examples/custom_memory.rs: add Default impl (new_without_default)
- examples/custom_channel.rs: fix needless_borrows_for_generic_args

src/skills/mod.rs

@@ -329,6 +329,7 @@ pub fn handle_command(command: super::SkillCommands, workspace_dir: &Path) -> Re
 }
 
 #[cfg(test)]
+#[allow(clippy::similar_names)]
 mod tests {
     use super::*;
     use std::fs;