dsh-failure-ledger: Add failure ledger and token savings panel to DSH sessions

dsh-failure-ledger is a TMrazbw-maintained DSH profile-level Host + Client plugin for workflow categorization, version V2.8 (package 0.1.2, 194 tests, MIT). It performs four main functions: compressing large tool errors into short summaries and logging them; tracking conversation anomalies across sessions (index.jsonl / INBOX.md / reports/<fingerprint>.md / failure_inbox); providing zero-token failure and savings reminders at the end of each round; and displaying a sidebar panel showing savings by model and conservative estimated amounts. Thirteen default Guards are used for observation and anti-recurrence hints (non-blocking). Key features include V2.5 self-healing, V2.6 context attribution and budgeting, V2.7 unstick and claimWithoutEvidence, and V2.8 automatic handoff when switching conversations. Installation is done using `plugin_manager install_bundle` pointing to the GitHub repository. For usage, open the panel with `/dfl-ui` or instruct the model to call `failure_inbox` or `open_failure_ledger`. The plugin runs with the privileges of the current DSH process. Before installing, users should read the source code and LICENSE. Monetary values are estimates based on local data only.