refactor: execution context and messaging options

[abdebek]

Summary

• add shared execution-context support across the core, extensions, messaging, audit, data-access, sample, and templates
• make template validation deterministic against local preview packages and Docker-backed durable scenarios
• PostgreSQL durable template apps no longer fail on SQL Server-specific identity index filters during startup
• move global error handling to the correct position in ApplicationBuilderExtensions.
• introduce MessagingExecutionContext for handling message-specific execution context.
• update MessagingOptions to include local queue name, queue prefix, and dead-letter expiration settings.
• enhance IRepository interface with default implementations for AnyAsync, SingleOrDefaultAsync, and CountAsync methods.
• add tests for ExecutionContext and MessagingOptions to ensure correct behavior and configuration.
• update AppDbContext to support execution context.

Why

A few problems in the current library surface:

• there was no shared execution-context abstraction for user, tenant, and correlation data
• audit, data access, HTTP flows, and Wolverine handlers were drifting toward separate context models
• some new public-surface changes on dev were source-breaking or under-documented
• generated template validation could be polluted by stale local package cache state
• provider-specific SQL leaked into shared identity data-access code

Changes

• add IExecutionContext, NullExecutionContext, and configurable ExecutionContextOptions
• add HTTP-backed and Wolverine-backed execution-context implementations
• align audit defaults to bridge from IExecutionContext while keeping IAuditContextProvider compatible
• add non-breaking execution-context constructor overloads to DbContextBase and IdentityDbContextBase
• add GetCurrentTenantId() alongside GetCurrentUserId() in data-access base contexts
• make IdentityDbContextBase provider-aware so SQL Server filtered-index syntax is not applied to PostgreSQL or SQLite
• reduce IRepository implementor breakage with default interface members and document them as compatibility fallbacks
• expand messaging options for queue naming, dead-letter expiration, and policy hooks
• make messaging execution-context registration explicit and configurable
• fix API middleware ordering in UseMinimalCleanArchApiDefaults
• update sample app, templates, and docs to use the newer defaults
• harden template validation by clearing stale local MCA package cache before scaffold validation

Behavioral fixes

• UserName resolution now prefers name claims over email claims
• built-in tenant resolution no longer assumes app-specific claim names such as business_id or organization_id
• execution metadata is cached per scoped execution-context instance instead of reallocating on each access
• messaging explicitly replaces the default execution-context registration instead of silently overriding it via duplicate scoped registrations

This batch fixes those issues while keeping the public API evolution additive and focused.