perf(agent): rombak alur AI agent — adaptif, hemat token, self-healing

Ganti explore phase MANDATORY (3 subagent tiap turn, boros) dengan
tool explore_codebase yang DIPUTUSKAN agent sendiri (lazy, token-aware):
- hapus ExploreService trait + with_explore + Phase 0 dari turn loop
- ExploreServiceImpl kini jadi tool 'explore_codebase' (1 context-scout
  subagent, read-only, cap output 4k chars)
- system prompt: instruksi TOKEN BUDGET (jawab langsung utk query simple,
  panggil explore_codebase sekali utk task kompleks)

Loop utama kini adaptif & self-healing:
- max_tokens adaptif (800/1600/4096 by request length) — bukan selalu 4096
- temperature 0.2 saat tool-calling, 0.7 utk final answer
- ErrorTracker: deteksi tool error berulang → inject recovery note,
  stop setelah 8 error total (bukan 50 iterasi sia-sia)
- auto-compact history > 60k chars sebelum LLM call
- tool output di-truncate ke 12k chars sebelum masuk konteks

Tambah 8 unit test (truncation, adaptive tokens, error tracker).

apps/application/src/agent/mod.rs

@@ -19,8 +19,6 @@ pub trait AgentTurnService: Send + Sync {
     fn run_turn(&self, params: AgentTurnParams) -> impl Future<Output = Result<()>> + Send;
 }
 
-pub mod explore;
 pub mod turn_service;
 
-pub use explore::{ExploreOutput, ExploreService};
 pub use turn_service::{compact_messages_with_ai, AgentTurnServiceImpl};