Reorganize repo: backend/, deploy/, docs/ layout + AGENTS.md

Restructure the monorepo into clear top-level directories:
- backend/: Go module root (cmd, internal, pkg, configs, migrations,
  docs/swagger, scripts, tests, go.mod, Makefile, .air.toml)
- deploy/: Docker (Dockerfile, docker-compose*), quickstart, fluentd
- docs/: project documentation + reports/ (moved from repo root)
- AGENTS.md: new AI coding-agent guide at repo root

Update all references to the new layout:
- Dockerfile: COPY backend/go.mod, COPY backend/ (context = repo root)
- docker-compose files: context ../.., dockerfile deploy/docker/Dockerfile,
  env_file ../../.env, volume mounts ../../backend:/app
- deploy/quickstart/compose.yaml: dockerfile deploy/docker/Dockerfile
- CI: working-directory: backend for go commands, file deploy/docker/Dockerfile,
  coverage path backend/coverage.out, health_check backend/scripts/
- backend/Makefile: docker target uses -f ../deploy/docker/Dockerfile ../
- README: architecture tree, quickstart, config paths updated

Move root stray scripts (rename_models.*, run_m11_tests.sh, verify_build.sh,
gorm_bool_main.go) to backend/scripts/legacy/. All moves via git mv to
preserve history. Build, vet, SQLite tests, and docker compose config verified.

backend/internal/service/llm_response_parser_test.go

@@ -0,0 +1,72 @@
+package service
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// ========== parseJSONResponse Tests ==========
+
+func TestParseJSONResponse_DirectJSON(t *testing.T) {
+	content := `{"suggestions": [{"labels": ["a", "b"], "priority": "high", "reason": "test reason"}]}`
+	var result LabelSuggestionResult
+	err := parseJSONResponse(content, &result)
+
+	require.NoError(t, err)
+	assert.Len(t, result.Suggestions, 1)
+	assert.Equal(t, "high", result.Suggestions[0].Priority)
+	assert.Len(t, result.Suggestions[0].Labels, 2)
+}
+
+func TestParseJSONResponse_MarkdownCodeBlock(t *testing.T) {
+	content := "```json\n{\"suggestions\": [{\"labels\": [\"test\"], \"priority\": \"low\", \"reason\": \"test reason\"}]}\n```"
+	var result LabelSuggestionResult
+	err := parseJSONResponse(content, &result)
+
+	require.NoError(t, err)
+	assert.Len(t, result.Suggestions, 1)
+	assert.Equal(t, "low", result.Suggestions[0].Priority)
+	assert.Equal(t, "test reason", result.Suggestions[0].Reason)
+}
+
+func TestParseJSONResponse_PlainCodeBlock(t *testing.T) {
+	content := "```json\n{\"suggestions\": [{\"labels\": [], \"priority\": \"medium\"}]}\n```"
+	var result LabelSuggestionResult
+	err := parseJSONResponse(content, &result)
+
+	require.NoError(t, err)
+	assert.Len(t, result.Suggestions, 1)
+	assert.Equal(t, "medium", result.Suggestions[0].Priority)
+}
+
+func TestParseJSONResponse_EmbeddedJSON(t *testing.T) {
+	content := "Here is the analysis:\n{\"participants\": [], \"summary\": \"test summary\"}\nEnd of analysis."
+	var result ParticipantAnalysisResult
+	err := parseJSONResponse(content, &result)
+
+	require.NoError(t, err)
+	assert.Equal(t, "test summary", result.Summary)
+}
+
+func TestParseJSONResponse_InvalidJSON(t *testing.T) {
+	content := "this is not json at all"
+	var result LabelSuggestionResult
+	err := parseJSONResponse(content, &result)
+
+	assert.Error(t, err)
+}
+
+func TestExtractLabelSuggestionFromText(t *testing.T) {
+	content := "Label: bug, feature\nPriority: high\nReason: urgent issue"
+	result := extractLabelSuggestionFromText(content)
+
+	assert.NotEmpty(t, result.Suggestions)
+	if len(result.Suggestions) > 0 {
+		assert.Contains(t, result.Suggestions[0].Labels, "bug")
+		assert.Contains(t, result.Suggestions[0].Labels, "feature")
+		assert.Equal(t, "high", result.Suggestions[0].Priority)
+		assert.Equal(t, "urgent issue", result.Suggestions[0].Reason)
+	}
+}