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/app/subagent/workspace.rs

@@ -0,0 +1,42 @@
+//! Workspace directory-tree generation for subagent system prompts.
+//!
+//! Build an ASCII tree of the workspace directory structure so the LLM
+//! can see the file layout.
+
+use std::fmt::Write;
+
+/// Build an ASCII tree of the workspace directory structure for the
+/// system prompt, so the LLM can see the file layout.
+///
+/// Flow: for each root, walk using `ignore::WalkBuilder` (respecting
+/// `.gitignore` and hidden files) → prefix `[DIR]` for directories →
+/// truncate after 1000 entries.
+pub(crate) fn generate_workspace_tree(roots: &[std::path::PathBuf]) -> String {
+    let mut out = String::new();
+    out.push_str("Current Workspace Directory Structure:\n");
+    for root in roots {
+        writeln!(out, "Root: {}", root.display()).unwrap();
+        let walker = ignore::WalkBuilder::new(root)
+            .hidden(true)
+            .git_ignore(true)
+            .build();
+        let mut count = 0;
+        for entry in walker.flatten() {
+            let path = entry.path();
+            if let Ok(rel) = path.strip_prefix(root) {
+                if rel.as_os_str().is_empty() {
+                    continue;
+                }
+                let is_dir = entry.file_type().is_some_and(|ft| ft.is_dir());
+                let prefix = if is_dir { "[DIR] " } else { "      " };
+                writeln!(out, "  {}{}", prefix, rel.display()).unwrap();
+                count += 1;
+                if count > 1000 {
+                    out.push_str("  ... (truncated)\n");
+                    break;
+                }
+            }
+        }
+    }
+    out
+}