fix(#999): resolve all clippy warnings across the workspace

All crates now pass `cargo clippy --workspace -- -D warnings` cleanly.

Fixes span six crates (hive-sh4re, hive-ag3nt, hive-c0re, hive-forge,
hive-priv, hive-matrix-mcp was already clean):

- doc_markdown: wrap snake_case, type names, constants in backticks
- collapsible_if / collapsible_match: fold nested ifs into let-chains
- duration_suboptimal_units: Duration::from_secs(N) → from_mins/from_hours
- implicit_hasher: allow on HashMap-param fns where generalization is risky
- items_after_statements: hoist use to function tops
- map(f).unwrap_or(x) → map_or(x, f); map(f).unwrap_or_else(g) → map_or_else
- is_ok_and / is_none_or in place of map().unwrap_or(bool)
- needless_continue: {} instead of continue in loop match arms
- match_same_arms: Ok(None) | Err(_) merged
- format_push_str: write!() instead of push_str(&format!())
- while let replaces loop { let Some(..) = x else { break } }
- struct_excessive_bools / dead_code: allow on purpose-built structs
- too_many_lines / too_many_arguments: allow where refactor not worth it
- unused_async: remove async from poll_once in bash_runner
- needless_borrow: fix &repo deref in hive-forge comments verb
- cast_possible_truncation: allow u64→usize in fetch_tail

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

hive-c0re/src/manager_server.rs

@@ -14,6 +14,7 @@ use crate::coordinator::Coordinator;
 use crate::lifecycle;
 
 pub fn start(coord: Arc<Coordinator>) -> Result<()> {
+    use std::os::unix::fs::PermissionsExt as _;
     let dir = Coordinator::manager_dir();
     std::fs::create_dir_all(&dir)
         .with_context(|| format!("create manager dir {}", dir.display()))?;
@@ -25,7 +26,6 @@ pub fn start(coord: Arc<Coordinator>) -> Result<()> {
         .with_context(|| format!("bind manager socket {}", socket.display()))?;
     // 0666 so the in-container root user (non-root) can connect;
     // the bind source dir is manager-only on host. See agent_server.rs.
-    use std::os::unix::fs::PermissionsExt as _;
     std::fs::set_permissions(&socket, std::fs::Permissions::from_mode(0o666))
         .with_context(|| format!("chmod manager socket {}", socket.display()))?;
     tracing::info!(socket = %socket.display(), "manager socket listening");