P1: consolidate agent metadata into Agent.Metadata() interface

[rsnodgrass]

Parent Epic

Part of #396 (unify agent abstraction layer)

Problem

Agent display names, CLI binary names, config paths, and type aliases are defined in 4+ separate locations:

Data	Locations
Display names	agent_hook.go:agentDisplayNames, hooks_user_marker.go:agentDisplayNames, prime/agent_type.go:AgentDisplayName(), each Agent's Name()
CLI binary names	doctor_integration.go:detect*(), agent_auth.go:CheckAgentUsability(), hooks_*.go
Config paths	doctor_integration.go:detect*(), hooks_user_marker.go:agentContextPaths, agent_auth.go
Type aliases	prime/agent_type.go:CanonicalAgentType(), adapters/*.go:init(), agent_hook.go:resolveAgentType()

Proposed Solution

Add a Metadata() method to the Agent interface:

type AgentMetadata struct {
    Type        string   // "claude-code"
    CLIBinary   string   // "claude"
    DisplayName string   // "Claude Code"
    ConfigPaths []string // paths to check for detection
    Aliases     []string // ["claude", "claude-code"]
}

All consumers read from the registry instead of maintaining local maps.

Files to Change

• cmd/ox/hooks_agent.go — add Metadata() to interface, implement on each agent struct
• cmd/ox/agent_hook.go — delete agentDisplayNames, derive from registry
• cmd/ox/hooks_user_marker.go — delete agentDisplayNames and agentContextPaths, derive from registry
• cmd/ox/doctor_integration.go — rewrite detect functions to use metadata
• internal/daemon/agentwork/agent_auth.go — use metadata instead of switch
• internal/prime/agent_type.go — AgentDisplayName() delegates to registry or deleted

Risk

• Blast radius: Medium (~8 files, mechanical changes)
• Behavior change: None — all consumers switch from local maps to registry lookups