Extract domain services into self-registering module types (feature flag pattern)

[intel352]

Overview

Following the template established by the feature flag migration (PR #56, commit ab64254), extract each domain service into a self-registering module type that can be declared in YAML config.

Template pattern:

1. Define the module type with config struct (db_path, cache_ttl, etc.)
2. Module's ProvidesServices() self-registers its admin adapter in the service registry
3. Server auto-discovers it via interface assertion — no explicit wiring

Domain Services to Extract

Service	Current Location	New Module Type	Key Config
Event Store	evstore.SQLiteEventStore	eventstore.service	db_path, retention_days
Timeline/Replay	store/timeline_handler.go	timeline.service	event_store dependency
DLQ	store/dlq_handler.go	dlq.service	max_retries, retention
Execution Tracker	module/execution_tracker.go	execution.tracker	event_store dependency
Runtime Manager	module/runtime_manager.go	runtime.manager	—
Backfill/Mock/Diff	store/backfill_handler.go	backfill.service	—
Ingest Handler	hardcoded in server	ingest.handler	—
Billing	billing/handler.go	billing.service	stripe_key, plans

Per-Service Pattern

For each service:

• Create module type in module/ (or reuse existing if partially done)
• Implement ProvidesServices() to self-register admin adapter
• Add config struct with appropriate fields
• Register factory in engine.go (or plugin)
• Declare in admin/config.yaml
• Remove hardcoded wiring from cmd/server/main.go
• Add schema in schema/module_schema.go
• Test module in isolation

Depends On

• Phase A (Admin Decomposition: Consolidate 18 handler modules into 2 generic handlers (Phase A) #85) for handler consolidation
• PR Refactor serverApp god object into domain-scoped sub-structs with minimal interfaces; move admin wiring to config+primitives #56 merged (feature flag template)

Already Done

• ✅ featureflag.service — PR Refactor serverApp god object into domain-scoped sub-structs with minimal interfaces; move admin wiring to config+primitives #56 (the template)