Refactor/sync command closures

[PTFOPlayer]

Merge pull request: Refactor command architecture + token tracking fixes

High-level:
Replace the monolithic Command enum with a trait-based CommandRegistry supporting lightweight sync closures. Convert all remaining async commands to async_command! macro. Fix two bugs: JSON numeric tool argument parsing and context-token undercounting.

Changes (refactor/sync-command-closures, 4 commits, -231 net lines):

1. a089f37 — Replace Command enum with trait-based registry + sync closures

   • Introduces Command trait, SyncCommand<F> wrapper, AliasCommand, and CommandRegistry in commands/registry.rs
   • Extracts CommandContext from the old CommandDispatcher
   • Converts all 18 sync commands from struct + impl Command to closures registered via register_sync() / register_sync_with_usage()
   • 6 async commands kept as impl Command, later converted in the next commit
   • Eliminates ~18 struct definitions and their impl Command boilerplate
   • Net -231 lines (1020 removed, 789 added); 87 tests pass, clippy clean

2. 69561db — Convert remaining async commands to async_command! macro

   • Converts CompactCommand, TimeoutCommand, RetriesCommand, ModelsCommand, InitCommand, ConfigSettingsCommand
   • Eliminates ~25 lines of boilerplate per async command
   • Net -105 lines (249 removed, 144 added)

3. e755f76 — Use Ollama prompt_eval_count for accurate context token tracking

   • Adjusts heuristic constants to better match real tokenizer behavior for tool output messages (Role::Tool was being undercounted)
   • Captures ground-truth prompt_eval_count from Ollama's final_data response, caching it alongside the message count at capture time
   • Falls back to heuristic only when messages have changed; invalidates cache after slash commands that mutate messages

4. 03aef90 — Handle JSON numeric tool arguments (timeout, etc.)

   • execute_tool_call used v.as_str() which returned None for JSON number values, silently producing "" that fell through parse::<u64>() to defaults
   • Fixes by matching on Value::String vs everything else, using to_string() for non-string values (numbers, booleans)