feat(ai): add Wafer Pass and Wafer Serverless providers

Wafer (https://wafer.ai) exposes a single OpenAI-compatible endpoint
(`https://pass.wafer.ai/v1`) for two SKUs whose entitlement differs
server-side, so we model them as two parallel providers — mirroring the
firepass/fireworks split so a user with both subscriptions can switch
without re-pasting:

- `wafer-pass` — flat-rate. `/v1/models` is filtered to entries whose
  `wafer.tier === "pass_included"`.
- `wafer-serverless` — pay-as-you-go superset of Pass.

Both issue `wfr_…` keys. `/login wafer-pass` and `/login wafer-serverless`
paste-and-validate via `/v1/models`. `WAFER_PASS_API_KEY` and
`WAFER_SERVERLESS_API_KEY` are wired through `getEnvApiKey`.

Bundled catalog:
- `wafer-pass`: GLM-5.1, Qwen3.5-397B-A17B.
- `wafer-serverless`: GLM-5.1, Qwen3.5-397B-A17B, Kimi-K2.6, Qwen3.6-35B-A3B.

Dynamic discovery via `/v1/models` overlays additional models at runtime
and folds the `wafer` envelope (tier, capabilities, cents/M pricing) into
the canonical `Model<"openai-completions">` shape. GLM-family entries
carry the zai-style thinking compat (`thinkingFormat: "zai"`,
`reasoningContentField: "reasoning_content"`) so reasoning tokens land in
the right field. Cents-per-million → dollars-per-million via /100.

Tests (`packages/ai/test/wafer.test.ts`, 5 cases): bundled catalog
contract for both providers and wire-id pass-through (case-sensitive,
no rewrite — `GLM-5.1` must round-trip verbatim or upstream 404s).
Optional `packages/ai/test/wafer.live.ts` exercises a real round-trip
against `pass.wafer.ai` when `WAFER_PASS_API_KEY` is set.

packages/coding-agent/src/cli/args.ts

@@ -247,6 +247,8 @@ export function getExtraHelpText(): string {
   OPENCODE_API_KEY           - OpenCode Zen/OpenCode Go models
   CURSOR_ACCESS_TOKEN        - Cursor AI models
   AI_GATEWAY_API_KEY         - Vercel AI Gateway
+  WAFER_PASS_API_KEY         - Wafer Pass (flat-rate subscription; GLM-5.1, Qwen3.5)
+  WAFER_SERVERLESS_API_KEY   - Wafer Serverless (pay-as-you-go)
 
   ${chalk.dim("# Cloud Providers")}
   AWS_PROFILE                - AWS Bedrock (or AWS_ACCESS_KEY_ID + AWS_SECRET_ACCESS_KEY)