refactor: split jobs_view, drop YAML migration, update docs (T6.1-T6.4)

T6.1: split jobs_view.go into three files — jobs_view_helpers.go (pure
helpers) and jobs_view_details.go (detailsPanel struct with widget
creation, update, clear, and container methods) — bringing jobs_view.go
from 459 to ~200 lines.

T6.2: remove stale YAML upgrade note from README; drop *.yaml from
.dockerignore.

T6.3: delete YAML shadow structs (yamlConfig/yamlJob/yamlJobsFile),
importYAMLConfig/importYAMLJobs, legacy path constants, and all
YAML-import tests; run go mod tidy to remove go.yaml.in/yaml/v4.

T6.4: refresh ARCHITECTURE.md — JSON storage references, new Key Domain
Concepts section (per-job overlap policy, run-time statistics + log
seeding, persisted pause flag, jobs_view split).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/ui/jobs_view_helpers.go

@@ -0,0 +1,57 @@
+package ui
+
+import "strings"
+
+// lastJobLogs returns a fresh slice of the most recent activity entries for the
+// "Selected job activity" panel. Logs are stored newest-first (see
+// app.Service.recordRun), so the leading entries are the latest; the result is
+// capped at maxJobActivityRows.
+func lastJobLogs(logs []event) []event {
+	n := len(logs)
+	if n > maxJobActivityRows {
+		n = maxJobActivityRows
+	}
+	return append([]event(nil), logs[:n]...)
+}
+
+func filteredJobIndexes(jobs []job, folder string) []int {
+	indexes := make([]int, 0, len(jobs))
+	for index, current := range jobs {
+		if folder == allFolders || filterValue(current.Folder) == folder {
+			indexes = append(indexes, index)
+		}
+	}
+	return indexes
+}
+
+func folderOptions(jobs []job) []string {
+	// "All" and "No folder" are always present so the filter UI is stable even
+	// before the user creates folders.
+	options := []string{allFolders, noFolder}
+	seen := map[string]bool{allFolders: true, noFolder: true}
+	for _, current := range jobs {
+		folder := strings.TrimSpace(current.Folder)
+		if folder == "" || seen[folder] {
+			continue
+		}
+		seen[folder] = true
+		options = append(options, folder)
+	}
+	return options
+}
+
+func filterValue(folder string) string {
+	if strings.TrimSpace(folder) == "" {
+		return noFolder
+	}
+	return strings.TrimSpace(folder)
+}
+
+func indexOfID(jobs []job, id int) int {
+	for index, current := range jobs {
+		if current.ID == id {
+			return index
+		}
+	}
+	return 0
+}