feat: add Pydantic models and EventEmitter for v2 core

- models.py: ProviderConfig, RoleConfig, DiscussionConfig, ScenarioConfig,
  Message, ToolCallRecord, Session — compatible with config.yaml format
- events.py: Event constants, Event dataclass, EventEmitter with on/off/emit
- 67 tests passing (37 models + 30 events)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

meeting_room/models.py

@@ -0,0 +1,124 @@
+"""Pydantic v2 data models for Meeting Room."""
+
+from __future__ import annotations
+
+from datetime import datetime, timezone
+from typing import Union
+
+from pydantic import BaseModel, ConfigDict, Field, field_validator
+
+
+# ---------------------------------------------------------------------------
+# Configuration models — must be compatible with config.yaml parsed by
+# yaml.safe_load() so that DiscussionConfig(**yaml_config) works unchanged.
+# ---------------------------------------------------------------------------
+
+
+class ProviderConfig(BaseModel):
+    """A single API provider (OpenAI-compatible endpoint)."""
+
+    model_config = ConfigDict(extra="forbid")
+
+    base_url: str
+    api_key: str
+
+
+class RoleConfig(BaseModel):
+    """A discussion participant role bound to a provider/model."""
+
+    model_config = ConfigDict(extra="forbid")
+
+    name: str
+    provider: str
+    model: str
+    temperature: float = 0.7
+    tools: Union[str, list[str]] = "none"
+    system_prompt: str = ""
+
+    @field_validator("tools", mode="before")
+    @classmethod
+    def _coerce_tools(cls, v: object) -> Union[str, list[str]]:
+        if isinstance(v, str):
+            return v
+        if isinstance(v, list):
+            return [str(item) for item in v]
+        raise ValueError(f"tools must be a string or list of strings, got {type(v).__name__}")
+
+
+class DefaultsConfig(BaseModel):
+    """Default settings inherited by scenarios."""
+
+    model_config = ConfigDict(extra="ignore")
+
+    max_rounds: int = 8
+    language: str = "ru"
+    framework: str = "custom"
+    workdir: str = "."
+
+
+class DiscussionConfig(BaseModel):
+    """Top-level config — the direct counterpart of config.yaml."""
+
+    model_config = ConfigDict(extra="ignore")
+
+    providers: dict[str, ProviderConfig] = Field(default_factory=dict)
+    roles: dict[str, RoleConfig] = Field(default_factory=dict)
+    defaults: DefaultsConfig = Field(default_factory=DefaultsConfig)
+
+
+# ---------------------------------------------------------------------------
+# Scenario model
+# ---------------------------------------------------------------------------
+
+
+class ScenarioConfig(BaseModel):
+    """A discussion scenario (loaded from .md / .yaml files)."""
+
+    model_config = ConfigDict(extra="ignore")
+
+    name: str = "Untitled"
+    participants: list[str] = Field(default_factory=list)
+    max_rounds: int = 8
+    problem: str = ""
+
+
+# ---------------------------------------------------------------------------
+# Runtime models
+# ---------------------------------------------------------------------------
+
+
+class Message(BaseModel):
+    """A single message in a discussion session."""
+
+    model_config = ConfigDict(extra="forbid")
+
+    role_id: str
+    name: str
+    content: str
+
+
+class ToolCallRecord(BaseModel):
+    """Record of a single tool call made by an agent."""
+
+    model_config = ConfigDict(extra="forbid")
+
+    id: str
+    name: str
+    arguments: str
+    result: str = ""
+
+
+class Session(BaseModel):
+    """A complete discussion session (scenario + messages + timestamps)."""
+
+    model_config = ConfigDict(extra="ignore")
+
+    scenario: ScenarioConfig = Field(default_factory=ScenarioConfig)
+    messages: list[Message] = Field(default_factory=list)
+    tool_calls: list[ToolCallRecord] = Field(default_factory=list)
+    created_at: datetime = Field(
+        default_factory=lambda: datetime.now(timezone.utc),
+    )
+    updated_at: datetime = Field(
+        default_factory=lambda: datetime.now(timezone.utc),
+    )