docs: remove stale AutoMapper references in architecture overview

[hokiepokedad2]

Observed

Spotted during PR #234 docs review.

`docs/architecture/overview.md:94-95` still talks about "AutoMapper for partial updates" and `.ForAllMembers(opts => ...)` despite AutoMapper having been removed from the project in v2.6.0 in favor of manual mapping extensions (`AlarmMappingExtensions`, `EntityMappingExtensions`).

`CLAUDE.md` has been updated correctly:

Mapping: Manual extension methods (`AlarmMappingExtensions`, `EntityMappingExtensions`) for Entity-to-Model and DTO-to-Model conversions (alarm CRUD uses JSON via PoracleNG proxy)

but `docs/architecture/overview.md` was missed.

Suggested fix

Replace the stale paragraph in `docs/architecture/overview.md:94-95` to describe the current mapping layer:

• Static extension methods in `Core.Mappings/`
• `AlarmMappingExtensions.To*()` / `ApplyUpdate()` for alarm DTOs
• `EntityMappingExtensions.ToModel()` / `ToEntity()` / `ApplyTo()` for Human, Profile, and PoracleWeb-owned tables
• Null-skip semantics on ApplyUpdate

Also grep `docs/**/*.md` for any other `AutoMapper` / `.ForAllMembers` references and purge them.