feat!: remove pre-GA compatibility surfaces

[pacphi]

Closes #83

Outcome

• removes ak dual, ak provider, and ak x provider; ak run and ak host are the sole GA surfaces
• migrates legacy routing, host, binding, and ownership intent once into versioned routing and integrations envelopes
• preserves host-less route defaults and legacy bindings without loss; conflicting binding IDs and unsupported envelopes fail closed with readable recovery
• removes dead compatibility helpers, usage aliases, dashboard fallbacks, executor dependencies, active legacy guidance, and retired package files
• preserves explicit OpenCode routing while keeping it non-primary and outside AQE projection
• adds ADR-0020, concise upgrading guidance, GA surface/package guards, and direct teardown/migration regression coverage

Verification

• pnpm run check
• coverage: 82.59% lines, 79.73% branches, 84.88% functions
• git diff --check
• package dry run: 127 files, zero retired/private/generated paths
• three independent read-only final audits: SHIP (legacy/package, OpenCode/canonical config, dependency/checklist)

Breaking migration

Removed commands now fail as unknown commands. Existing configuration is normalized in memory on load and persists only when a command explicitly saves it. See docs/UPGRADING.md for replacements and manual cleanup guidance for old unreceipted adapter installs.