phase-40: Gemini + Claude provider adapters

Phase 40 PRD (docs/CONTROL_PLANE_PRD.md:82-83) listed:
  - crates/aibridge/src/providers/gemini.rs
  - crates/aibridge/src/providers/claude.rs

Neither existed. Landing both now, in gateway/src/v1/ (matches the
existing ollama.rs + openrouter.rs sibling pattern — aibridge's
providers/ is for the adapter *trait* abstractions, v1/ holds the
concrete /v1/chat dispatchers that know the wire format).

gemini.rs:
  - POST https://generativelanguage.googleapis.com/v1beta/models/
    {model}:generateContent?key=<API_KEY>
  - Auth: query-string key (not bearer)
  - Maps messages → contents+parts (Gemini's wire shape),
    extracts from candidates[0].content.parts[0].text
  - 3 tests: key resolution, body serialization (camelCase
    generationConfig + maxOutputTokens), prefix-strip

claude.rs:
  - POST https://api.anthropic.com/v1/messages
  - Auth: x-api-key header + anthropic-version: 2023-06-01
  - Carries system prompt in top-level `system` field (not
    messages[]). Extracts from content[0].text where type=="text"
  - 4 tests: key resolution, body serialization with/without
    system field, prefix-strip

v1/mod.rs:
  + V1State.gemini_key + claude_key Option<String>
  + resolve_provider() strips "gemini/" and "claude/" prefixes
  + /v1/chat dispatcher handles "gemini" + "claude"/"anthropic"
  + 2 new resolve_provider tests (prefix + strip per adapter)

main.rs:
  + Construct both keys at startup via resolve_*_key() helpers.
    Missing keys log at debug (not warn) since these are optional
    providers — unlike OpenRouter which is the rescue rung.

Every /v1/chat error path mirrors the existing pattern:
  - 503 SERVICE_UNAVAILABLE when key isn't configured
  - 502 BAD_GATEWAY with the provider's error text when the
    upstream call fails
  - Response shape always the OpenAI-compatible ChatResponse

Workspace warnings still at 0. 9 new tests pass.

Pre-existing test failure `executor_prompt_includes_surfaced_
candidates` at execution_loop/mod.rs:1550 is unrelated (fails on
pristine HEAD too — PR fixture divergence).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Cargo.lock

@@ -8906,6 +8906,17 @@ dependencies = [
  "wasm-bindgen",
 ]
 
+[[package]]
+name = "validator"
+version = "0.1.0"
+dependencies = [
+ "serde",
+ "serde_json",
+ "thiserror 2.0.18",
+ "tokio",
+ "tracing",
+]
+
 [[package]]
 name = "valuable"
 version = "0.1.1"