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-forge/src/verbs/diff.rs

@@ -144,8 +144,7 @@ fn parse_diff_git_path(rest: &str) -> Option<String> {
         // containing `"` doesn't terminate early).
         let mut iter = after_open.char_indices();
         let mut a_close = None;
-        loop {
-            let Some((i, c)) = iter.next() else { break };
+        while let Some((i, c)) = iter.next() {
             if c == '\\' {
                 // Skip the next char — it's part of the escape.
                 iter.next();
@@ -167,8 +166,7 @@ fn parse_diff_git_path(rest: &str) -> Option<String> {
         // Find b-side's closing quote with the same escape rule.
         let mut iter = b_inside.char_indices();
         let mut b_close = None;
-        loop {
-            let Some((i, c)) = iter.next() else { break };
+        while let Some((i, c)) = iter.next() {
             if c == '\\' {
                 iter.next();
                 continue;