fix(kon): normalise British English table, single-pass whitespace collapse, byte-index safety

- Normalise BRITISH_REPLACEMENTS: remove baked-in \b from entries so all
  entries are plain base words; the function adds boundaries uniformly
- Replace O(n*m) while-loop double-space removal with single-pass collapse
- Add debug_assert! documenting ASCII assumption for byte-indexed suffix slicing
- Expand llm_client.rs module-level doc comment
- Run cargo fmt on ai-formatting crate

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

crates/ai-formatting/src/lib.rs

@@ -3,6 +3,4 @@ pub mod pipeline;
 pub mod rule_based;
 
 pub use pipeline::{post_process_segments, FormatMode, PostProcessOptions};
-pub use rule_based::{
-    format_text, is_hallucination, remove_fillers, to_british_english,
-};
+pub use rule_based::{format_text, is_hallucination, remove_fillers, to_british_english};