refactor: massive codebase restructuring — naming, splitting, DRY

Crate renames:
  - zesdex-entities::seaorm → domain (misleading name, no SeaORM used)
  - zesdex-dto → merged into zesdex-entities (100% re-exports)
  - zesdex-libs → zesdex-infra (vague name)

Module renames:
  - app/harness → guard (misleading: safety gatekeeper, not test harness)
  - runtime/commands → action_dispatch (name clashed with controller/command)
  - resources → prompts (embedded prompt text, not general resources)
  - tool/seqthink → sequential_think (unreadable abbreviation)
  - msglog/query → insert (module only inserts, never queries)

Dead code removal:
  - app/mode/help.rs (orphaned — not declared in mod.rs)
  - app/mode/loading.rs (orphaned — not declared in mod.rs)

File splitting (71 new files, avg ~115 lines/file):
  - app/runtime/actions/: 1→8 files (was 2030 lines)
  - view/overlays/: 1→16 files (was 1167 lines)
  - tool/lsp/: 1→8 per-tool files (was 909 lines)
  - main.rs: 1→5 files (session, daemon, attach, event_loop)
  - workflow/engine + hive_mind: 2→10 files
  - subagent/engine + auto: 2→9 files
  - lsp/provisioner: 1→5 files
  - review/: 1→6 files
  - guard/: 1→2 files (extracted patterns)
  - state/misc: 1→3 files (input, scroll)
  - mcp/: 1→3 files (transport, adapter)
  - stream/json_repair extracted from turn.rs

DRY:
  - Pattern constants (STUB_PATTERNS etc) in guard/patterns shared with subagent
  - 3 near-identical background spawners → 1 generic + thin wrappers
  - Shared spawn_subagent_with_drain() extracted
  - Shared create_session() in main
  - write_osc52 deduplicated

Bug fixes:
  - archive_message(): sess.db → db (wrong variable name)
  - execute_one_tool(): wrong parameter name
  - check_credential_read() function was missing (restored from test expectations)

crates/zesdex-backend/src/bin/migrate.rs

@@ -2,7 +2,7 @@
 use std::path::Path;
 
 fn main() -> anyhow::Result<()> {
-    let store = zesdex_entities::seaorm::common::store::Store::new();
+    let store = zesdex_entities::domain::common::store::Store::new();
 
     // Find all session directories
     let sessions_dir = store.base_dir.join("sessions");

crates/zesdex-backend/src/bin/seed.rs

@@ -2,7 +2,7 @@
 //! and app_config, and populates a default session for development.
 
 fn main() -> anyhow::Result<()> {
-    let store = zesdex_entities::seaorm::common::store::Store::new();
+    let store = zesdex_entities::domain::common::store::Store::new();
     store.ensure_dirs()?;
     tracing::info!("Store directories created at {:?}", store.base_dir);
 
@@ -45,7 +45,7 @@ fn main() -> anyhow::Result<()> {
 
     // Create a seed session
     let session_id = uuid::Uuid::new_v4().to_string();
-    let session = zesdex_entities::seaorm::auth::session::Session::new(
+    let session = zesdex_entities::domain::auth::session::Session::new(
         session_id.clone(),
         "Seed Session".to_string(),
     );