[Change] Architecture documentation discrepancies remediation

[djm81]

Why

The architecture discrepancies report (docs/architecture/discrepancies-report.md) identified conflicts between documentation, codebase, and OpenSpec (module system status, BridgeAdapter and layer documentation gaps, missing development guides, and spec-code expectation mismatches). This causes contributor confusion and hides current feature readiness.

What Changes

• Update architecture/reference docs to reflect current implementation accurately.
• Document full BridgeAdapter interface and ToolCapabilities usage.
• Add ADR template and initial ADR.
• Add module and adapter development guides.
• Add implementation status doc for implemented vs planned features with OpenSpec pointers.
• Align terminology, version references, and diagrams with real components.

OpenSpec Change Proposal: arch-08-documentation-discrepancies-remediation