Fix output truncation bug, add language support for agent responses

Bug 1 — Output truncation:
  _run_claude() was replacing raw stdout with parsed sub-field which
  could be a dict (not string). run_agent() then saved dict.__repr__
  to DB instead of full JSON. Fixed: _run_claude() always returns
  string output; run_agent() ensures string before DB write.
  Added tests: full_output_saved_to_db, dict_output_saved_as_json_string.

Bug 2 — Language support:
  Added projects.language column (TEXT DEFAULT 'ru').
  Auto-migration for existing DBs (ALTER TABLE ADD COLUMN).
  context_builder passes language in project context.
  format_prompt() appends "## Language\nALWAYS respond in {language}"
  at the end of every prompt.
  CLI: kin project add --language ru (default: ru).
  Tests: language in prompt for ru/en, project creation, context.

112 tests, all passing. ~/.kin/kin.db migrated (vdol: language=ru).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/test_context_builder.py

@@ -131,3 +131,33 @@ class TestFormatPrompt:
         ctx = build_context(conn, "VDOL-001", "analyst", "vdol")
         prompt = format_prompt(ctx, "analyst")  # No analyst.md exists
         assert "analyst" in prompt.lower()
+
+    def test_format_includes_language_ru(self, conn):
+        ctx = build_context(conn, "VDOL-001", "debugger", "vdol")
+        prompt = format_prompt(ctx, "debugger", "Debug.")
+        assert "## Language" in prompt
+        assert "Russian" in prompt
+        assert "ALWAYS respond in Russian" in prompt
+
+    def test_format_includes_language_en(self, conn):
+        # Update project language to en
+        conn.execute("UPDATE projects SET language='en' WHERE id='vdol'")
+        conn.commit()
+        ctx = build_context(conn, "VDOL-001", "debugger", "vdol")
+        prompt = format_prompt(ctx, "debugger", "Debug.")
+        assert "ALWAYS respond in English" in prompt
+
+
+class TestLanguageInProject:
+    def test_project_has_language_default(self, conn):
+        p = models.get_project(conn, "vdol")
+        assert p["language"] == "ru"
+
+    def test_create_project_with_language(self, conn):
+        p = models.create_project(conn, "en-proj", "English Project", "/en",
+                                  language="en")
+        assert p["language"] == "en"
+
+    def test_context_carries_language(self, conn):
+        ctx = build_context(conn, "VDOL-001", "pm", "vdol")
+        assert ctx["project"]["language"] == "ru"