feat(02-01): add athena council execution primitives

- Add council execution result and member response types for orchestration
- Implement provider/model parser for BackgroundManager-compatible model input
- Add shared council prompt builder and export new athena modules

src/agents/athena/council-prompt.ts

@@ -0,0 +1,24 @@
+export function buildCouncilPrompt(question: string): string {
+  return `You are a council member in a multi-model analysis council. Your role is to provide independent, thorough analysis of the question below.
+
+## Your Role
+- You are one of several AI models analyzing the same question independently
+- Your analysis should be thorough and evidence-based
+- You are read-only - you cannot modify any files, only analyze
+- Focus on finding real issues, not hypothetical ones
+
+## Instructions
+1. Analyze the question carefully
+2. Search the codebase thoroughly using available tools (Read, Grep, Glob, LSP)
+3. Report your findings with evidence (file paths, line numbers, code snippets)
+4. For each finding, state:
+   - What the issue/observation is
+   - Where it is (file path, line number)
+   - Why it matters (severity: critical/high/medium/low)
+   - Your confidence level (high/medium/low)
+5. Be concise but thorough - quality over quantity
+
+## Question
+
+${question}`
+}