Redesign ProxyFeatures API architecture

[remdui]

Summary

Implements the ProxyFeatures 3.3.0 clean API reset and completes the architecture, runtime, testing, and documentation work from the redesign plan.

Architecture

• separates the dependency-free public API, reusable toolkit, wire-only contracts, and Velocity runtime
• makes the plugin instance the authoritative ProxyFeaturesApi
• replaces reflective discovery and feature metadata companions with an explicit typed 33-feature manifest
• validates dependencies before startup and uses topological startup with reverse-order shutdown
• owns capability and extension registrations through feature lifecycle scopes
• removes the legacy discovery, service-directory, duplicate API implementation, compatibility, and runtime migration paths
• enforces that feature implementations do not import one another

API and runtime

• adds typed capabilities, lifecycle-safe CapabilityRef, immutable DTOs, stable identifiers, and explicit extension points
• narrows the contracts module to the seven cross-process wire messages
• moves reusable HTTP, configuration, cache, localization, text, JSON, and pagination support into focused toolkit packages
• hardens configuration list mutation, feature reload behavior, sanctions filtering/time handling, VersionCheck configuration, and CommandRelay durability tests
• distinguishes feature-local soft reloads from full framework lifecycle reloads in acceptance coverage

Validation

Exact-head checks on 6478dae6a2688806e839cf8bf1226279c361e733 are green:

• CI lint, Checkstyle, and shell/release-script validation
• full ./mvnw -U -B -ntp verify reactor
• 18 API tests
• 65 toolkit tests
• 21 contracts tests
• 815 Velocity tests
• JaCoCo coverage enforcement
• dependency convergence, upper-bound, declaration, and duplicate-class checks
• architecture and public-surface boundary tests
• API, toolkit, contracts, and distribution JAR-content audits
• external consumer compilation against public artifacts only
• real Velocity startup, command persistence, soft reload, lifecycle reload, capability replacement, manual-state cleanup, and clean shutdown

Breaking changes

This is an intentional 3.3.0 clean break. Legacy shims, compatibility adapters, reflection-based feature discovery, and runtime migration readers are not retained.

See docs/MIGRATING-3.3.md, docs/API.md, docs/ARCHITECTURE.md, and docs/API-REDESIGN-VALIDATION.md.