list_files with_metadata mode, deeper JSON outline, MCP connector descriptions in prompt

- list_files: new with_metadata parameter returns {path, line_count?, size}
  per entry (both disk and memory-docs) so the agent can spot large files
  worth outlining before reading
- ast_outline: replaced flat tree-sitter JSON walker with a recursive one
  that shows nested keys at every depth, with inline scalar values and
  container summaries
- message_builder: format active MCP connectors as a table with description
  instead of a bare bullet list
- read_file description now hints to use get_ast_outline first
- tools.md: agent guidance to outline before reading

crates/skald-core/src/db/memory_docs.rs

@@ -34,6 +34,16 @@ pub struct MemoryHit {
     pub snippet: String,
 }
 
+/// A directory listing row carrying cheap size metadata. `line_count` and
+/// `byte_len` are computed in SQL (`LENGTH` / newline count) so the note body
+/// never leaves the database.
+#[derive(Debug, Clone, sqlx::FromRow)]
+pub struct MemoryEntryMeta {
+    pub path:       String,
+    pub line_count: i64,
+    pub byte_len:   i64,
+}
+
 const SELECT: &str = "SELECT id, path, content, created_at, updated_at FROM memory_docs";
 
 /// Fetch one note by its exact path.
@@ -84,6 +94,27 @@ pub async fn list(pool: &SqlitePool, prefix: &str) -> Result<Vec<MemoryEntry>> {
     Ok(rows)
 }
 
+/// Like [`list`], but each row also carries a line count and byte length,
+/// computed in SQL so the body is never transferred. Line count matches the
+/// on-disk convention: an empty note is 0 lines, otherwise newline-count + 1.
+pub async fn list_with_metadata(pool: &SqlitePool, prefix: &str) -> Result<Vec<MemoryEntryMeta>> {
+    let pattern = format!("{}%", escape_like(prefix));
+    let rows = sqlx::query_as::<_, MemoryEntryMeta>(
+        "SELECT path,
+                CASE WHEN content = '' THEN 0
+                     ELSE LENGTH(content) - LENGTH(REPLACE(content, char(10), '')) + 1
+                END AS line_count,
+                LENGTH(CAST(content AS BLOB)) AS byte_len
+         FROM memory_docs
+         WHERE path LIKE ? ESCAPE '\\'
+         ORDER BY updated_at DESC",
+    )
+    .bind(pattern)
+    .fetch_all(pool)
+    .await?;
+    Ok(rows)
+}
+
 /// Full-text search over note bodies and paths, best match first. `query` is
 /// FTS5 MATCH syntax; `snippet` is a short excerpt of the body with the matched
 /// terms wrapped in `[` … `]`.