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-ag3nt/src/forge_notify.rs

@@ -88,8 +88,7 @@ pub async fn run(socket: PathBuf) {
     // HIVE_FORGE_KEEP_SUBSCRIPTIONS=1 disables auto-unsubscribe for agents
     // that intentionally consume the full repo notification firehose (e.g. triage).
     let keep_subscriptions = std::env::var("HIVE_FORGE_KEEP_SUBSCRIPTIONS")
-        .map(|v| v == "1" || v.eq_ignore_ascii_case("true"))
-        .unwrap_or(false);
+        .is_ok_and(|v| v == "1" || v.eq_ignore_ascii_case("true"));
 
     // Optional reason drop-list — comma-separated Forgejo `reason`
     // values to silently mark-read instead of deliver. See
@@ -159,7 +158,7 @@ fn notif_type_label(t: &str) -> &str {
 /// inside the forge-notify wrapper, so a leading `## title` line
 /// doesn't blow into an h2 in the dashboard render. See
 /// `docs/forge.md::Body excerpt + truncation + heading escape` for
-/// the strict-ATX-vs-`#tag` rationale and the split_inclusive
+/// the strict-ATX-vs-`#tag` rationale and the `split_inclusive`
 /// trailing-newline contract.
 fn escape_md_headings(body: &str) -> String {
     let mut out = String::with_capacity(body.len());