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/storage/paths.go

@@ -14,10 +14,6 @@ const (
 	// installed/copied program.
 	JobsFileName = "jobs.json"
 
-	// Legacy YAML file names used by builds before the JSON migration. These are
-	// read once on first start (P1.4) and then replaced by the JSON equivalents.
-	legacyYAMLConfigFileName = "gosentry.yaml"
-	legacyYAMLJobsFileName   = "jobs.yaml"
 )
 
 // Paths contains both the physical program location and the resolved runtime