feat(council): add council advisory skill with parallel/sequential/debate flows

- 3 advisors (Pragmatist, Visionary, Skeptic) + 1 Referee subagent
- Default: parallel + synthesis flow
- Prompt templates in references/prompts.md
- Model tier selection based on topic complexity
- Added TODO tasks for personality depth and skill name revisit

skills/council/SKILL.md

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+---
+name: council
+description: "Convene a council of AI advisor agents with distinct perspectives to deliberate on a topic, then synthesize their views into a verdict. Use when: (1) user asks for multi-perspective analysis, (2) wants to brainstorm with diverse viewpoints, (3) requests a council or advisors opinion, (4) needs a balanced decision on a complex question. Supports parallel (default), sequential, and debate flows. NOT for: simple factual lookups, single-perspective tasks, or quick one-liner answers."
+---
+
+# Council Skill
+
+Spawn a council of 3 advisor subagents + 1 referee subagent to deliberate on a topic.
+Each advisor has a distinct personality/lens. The referee synthesizes their output into a
+final verdict with collapsed advisor perspectives.
+
+## Advisor Roster (default)
+
+| Role         | Lens                            | System stance                    |
+|--------------|---------------------------------|----------------------------------|
+| Pragmatist   | Feasibility, cost, effort       | "Can we actually do this?"       |
+| Visionary    | Long-term potential, innovation | "What if we went bigger?"        |
+| Skeptic      | Risk, failure modes, edge cases | "What could go wrong?"           |
+
+The referee is a separate agent: balanced, fair, synthesis-oriented.
+
+## Flows
+
+Three deliberation flows are available. Default is **parallel**.
+
+### 1. Parallel + Synthesis (default)
+
+1. Spawn all 3 advisors simultaneously via `sessions_spawn` (mode=run).
+2. Each advisor receives the same topic prompt with their personality instructions.
+3. Wait for all 3 to complete (push-based — they announce when done).
+4. Spawn the referee with all 3 advisor outputs as context.
+5. Referee produces the final verdict.
+
+### 2. Sequential Rounds
+
+1. Spawn advisors one at a time, each seeing prior advisor outputs.
+2. After all advisors, spawn referee with full thread.
+3. Optionally run a rebuttal round (advisors respond to each other).
+
+### 3. Debate
+
+1. Spawn advisors in parallel for initial takes.
+2. Share outputs across advisors for rebuttals (1-2 rounds).
+3. Referee moderates and calls convergence.
+
+## Model Selection
+
+Pick model tier based on topic complexity:
+
+- **Light topics** (casual brainstorm, simple pros/cons): use default model for advisors and referee.
+- **Medium topics** (architecture decisions, strategy): use default model for advisors, stronger model for referee.
+- **Heavy topics** (critical decisions, deep analysis): use stronger model for all agents.
+
+The caller (main agent) determines tier before spawning.
+
+## Prompt Templates
+
+See `references/prompts.md` for full advisor and referee prompt templates with placeholders.
+
+## Implementation
+
+Read `scripts/council.sh` for the orchestration logic.
+For programmatic invocation, the main agent can also call `sessions_spawn` directly
+following the patterns above.
+
+## Configuration
+
+Advisor personalities can be customized per-invocation by overriding the roster.
+Default roster and prompt templates live in `references/prompts.md`.
+
+## TODO (revisit later)
+- Revisit subagent personality depth — richer backstories, communication styles
+- Revisit skill name — "council" works for now