feat(domain,infra,app): rotation/rétention log.jsonl + lecture paginée (LS6)

Backend uniquement (UI React repoussée à LS7) :
- domain : port ConversationArchive + structs SegmentStats/PageCursor/PageDirection/
  TurnSlice/RotationDecision/RotationThresholds, fn pures rotation_plan/clamp_page_limit
  + consts ; re-exports lib.
- infrastructure : impl ConversationArchive pour FsConversationLog (stats/rotate/page
  + helpers), archive segmentée hors chemin chaud.
- application : ReadConversationPage + DTO + ConversationArchiveProvider (conversation/paginate),
  RotateConversationLog (conversation/rotate), exports mod/lib.
- app-tauri : AppConversationArchiveProvider + wiring (state), rotation détachée dans
  launch_agent + commande read_conversation_page (commands), DTOs (dto),
  commande enregistrée (generate_handler!).
- tests (QA, verts) : conversation_log, conversation_rotate_paginate (nouveau),
  dto (module test). Pivots INV-LS6 et cohérence fold-après-rotation verts.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

crates/domain/src/lib.rs

@@ -103,8 +103,11 @@ pub use readiness::{ReadinessPolicy, ReadinessSignal};
 pub use session_limit::{plan_resume, RateLimitSource, ResumePlan, SessionLimit};
 
 pub use conversation_log::{
-    bound_handoff_summary, ConversationLog, ConversationTurn, Handoff, HandoffStore,
-    HandoffSummarizer, ProviderSessionStore, TurnId, TurnRole, HANDOFF_SUMMARY_MAX_CHARS,
+    bound_handoff_summary, clamp_page_limit, rotation_plan, ConversationArchive, ConversationLog,
+    ConversationTurn, Handoff, HandoffStore, HandoffSummarizer, PageCursor, PageDirection,
+    ProviderSessionStore, RotationDecision, RotationThresholds, SegmentStats, TurnId, TurnRole,
+    TurnSlice, HANDOFF_SUMMARY_MAX_CHARS, MAX_ARCHIVE_SEGMENTS, PAGE_DEFAULT_LIMIT, PAGE_MAX_LIMIT,
+    ROTATE_AFTER_BYTES, ROTATE_AFTER_TURNS,
 };
 
 pub use fileguard::{