compat: baked CC version constants package

[buildoak]

Summary

New compat/ package holding known-stable version constants. Single source of truth for version compatibility checks across CLI, startup warnings, and skill references.

Design

package compat

const KnownStableCC  = "2.1.78"
const KnownStableWet = "0.1.5"
const ValidatedDate  = "2026-03-18"

// CheckCCVersion compares installed CC against known-stable.
// Returns: match, newer, older, or not-found.
func CheckCCVersion() VersionStatus { ... }

// CheckClaudeApp returns whether Claude Desktop is running.
func CheckClaudeApp() bool { ... }

Update Protocol

When a new CC version is validated:

1. Bump KnownStableCC constant
2. Update ValidatedDate
3. Update skill/references/cc-compatibility.md matrix
4. Release wet

Context

This package is consumed by:

• wet check CLI subcommand
• wet claude startup warnings
• Skill diagnostic reference (cc-compatibility.md carries same values for agent-readable diagnostics)