Use CanopyWave Kimi K2.6 as base2-free model

[jahooma]

Summary

• Switch base2-free (and editor-lite, code-reviewer-lite) from Fireworks GLM 5.1 to CanopyWave Kimi K2.6
• Wire CanopyWave routing in the web chat-completions endpoint (was previously dead-coded behind `useCanopyWave = false`)
• Add per-model pricing in canopywave.ts so kimi-k2.6 is billed correctly
• Update freebuff model registry, free-mode whitelist, instant-admit capacity, and rate limits

Test plan

• `bun tsc --noEmit` passes for web, common, agents, cli
• `web/src/server/free-session` tests pass
• `web/src/app/api/v1/chat/completions/tests/completions.test.ts` passes (now asserts CanopyWave routing)
• `web/src/app/api/v1/freebuff/session/tests/session.test.ts` passes
• `agents/tests/editor.test.ts` passes
• `cli/src/utils/tests/freebuff-model-navigation.test.ts` passes
• Smoke-test end-to-end: `bun scripts/test-canopywave.ts both` against a running web instance

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