docs: align CLAUDE.md/AGENTS.md/README with the two-repo architecture; drop dead LLM routing

The LLM decision routing moved to the external Python backend
(OpenSquawk-LiveATC-api), but the core docs still described the old in-Nuxt
path (routeDecision(), /api/llm/decide, a Nuxt /api/decision-flows/runtime
route) — none of which exist. Every agent session started with a wrong mental
model.

- Rewrite CLAUDE.md to describe the real /pm flow (useRadioBackend -> Python
  backend owns authoritative state; Nuxt owns STT/TTS/audio/auth/editor) and
  fix stale commands (bun -> yarn).
- Fix the two stale AGENTS.md lines (openai.ts is getOpenAIClient() only;
  decisionFlowService is editor-only, no Nuxt runtime route).
- README: note the Python backend is required for /pm; correct server/ desc.
- Remove dead shared/utils/openaiDecision.ts (called the non-existent
  /api/llm/decide) and the now-orphaned LLM decision contract types in
  shared/types/llm.ts. Trace types used by pm.vue are kept.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

shared/utils/openaiDecision.ts

@@ -1,10 +0,0 @@
-// utils/openaiDecision.ts
-import type { LLMDecisionInput, LLMDecisionResult } from '../types/llm'
-
-/** Client-seitig: ruft den Backend-Endpunkt auf */
-export async function decideNextStateLLM(input: LLMDecisionInput): Promise<LLMDecisionResult> {
-    return await $fetch<LLMDecisionResult>('/api/llm/decide', {
-        method: 'POST',
-        body: input
-    })
-}