feat(agent): store durable agents in agents.db

[codeaholicguy]

Motivation

Store the new durable-agent capability directly in the existing SQLite database with durable session behavior and consistent Durable* domain vocabulary. JSON persistence was never released to users, so this PR intentionally contains no legacy import or compatibility path.

Design

• adds a separate flattened durable_agents table with case-insensitive durable names, provider/session identity, lifecycle and health state, latest-result columns, and atomic active-run ownership columns
• keeps durable rows isolated from the short-lived agents registry and its process pruner
• uses BEGIN IMMEDIATE transactions and token/start-time compare-and-swap updates for acquisition, provider recording, completion, and reconciliation
• makes readonly DatabaseConnection construction genuinely write-free and readonly listing pure
• exposes dbPath for isolated/direct repository construction; all tests use explicit SQLite paths
• standardizes the persistence API on DurableAgentRepository, matching the existing TaskRepository convention for durable SQLite domains

Scope

There is no print-agents.json import, marker row, backup rename, dual-write, rollback workflow, or filePath compatibility option. The unreleased JSON implementation and its tests were removed by product-owner direction.

The CLI mechanism flag remains --mode print, and Claude-specific provider names such as ClaudePrintRunner, ClaudePrintAgentService, and ClaudeCliProbe remain unchanged.

Validation

• focused repository/service suites: 16 tests passed; focused CLI suite: 74 tests passed
• agent-manager suite: 548 tests passed
• full pre-commit hook: lint plus 1,019 workspace tests passed
• full workspace typecheck and build passed
• feature documentation lint passed
• strict packages/docs sweep found no legacy DurableAgentStore names or durable-domain Store error/API references

Risks

None known beyond normal SQLite schema rollout for a new, unreleased feature.