feat: add Settings and Suite pages with comprehensive settings management and question suite builder

- Implemented SettingsPage for configuring default provider, temperature, and model paths.
- Added SuitePage for managing a suite of questions with features to add, edit, duplicate, and delete questions.
- Introduced TypeScript configuration files for app and node environments.
- Set up Vite configuration for development server with API proxying to backend.

plugin_api.py

@@ -0,0 +1,117 @@
+"""Stable types passed to LM-Gambit plugins.
+
+Plugins import from this module and nothing else in the project::
+
+    from plugin_api import Grade, RunRecord, TestRecord
+
+Everything here is a plain frozen dataclass, so plugins never touch engine or
+server internals and keep working across refactors of either.
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass, field
+from pathlib import Path
+from typing import Any, Dict, List, Optional
+
+__all__ = ["Grade", "GradeEntry", "RunRecord", "TestRecord", "PluginInfo"]
+
+
+@dataclass(frozen=True)
+class TestRecord:
+    """One question and the model's answer to it."""
+
+    index: int
+    total: int
+    title: str
+    filename: str
+    prompt: str
+    ok: bool
+    response: Optional[str] = None
+    error: Optional[str] = None
+    metrics: Dict[str, Any] = field(default_factory=dict)
+    elapsed: float = 0.0
+
+    @property
+    def tokens_per_second(self) -> float:
+        return float(self.metrics.get("tokens_per_second", 0) or 0)
+
+    @property
+    def total_tokens(self) -> int:
+        return int(self.metrics.get("total_tokens", 0) or 0)
+
+    @property
+    def time_to_first_token(self) -> float:
+        return float(self.metrics.get("time_to_first_token", 0) or 0)
+
+
+@dataclass(frozen=True)
+class Grade:
+    """A score for one answer.
+
+    ``score`` is clamped to 0.0–1.0. Return ``None`` from a grader instead of a
+    ``Grade`` to abstain — abstentions never count against the average.
+    """
+
+    score: float
+    label: str = ""
+    notes: str = ""
+
+    def __post_init__(self) -> None:
+        object.__setattr__(self, "score", max(0.0, min(1.0, float(self.score))))
+
+
+@dataclass(frozen=True)
+class GradeEntry:
+    """A grade together with the plugin that produced it."""
+
+    grader: str
+    grade: Grade
+
+
+@dataclass(frozen=True)
+class RunRecord:
+    """A whole diagnostic run, handed to lifecycle and report hooks."""
+
+    id: str
+    provider: str
+    model_id: str
+    model_label: str
+    temperature: float
+    total: int
+    status: str
+    started_at: float
+    finished_at: Optional[float] = None
+    report_path: Optional[Path] = None
+    summary: Dict[str, Any] = field(default_factory=dict)
+    tests: List[TestRecord] = field(default_factory=list)
+    grades: Dict[int, List[GradeEntry]] = field(default_factory=dict)
+
+    def score_for(self, test_index: int) -> Optional[float]:
+        """Mean score across every grader that scored this question."""
+        entries = self.grades.get(test_index) or []
+        if not entries:
+            return None
+        return sum(entry.grade.score for entry in entries) / len(entries)
+
+    @property
+    def overall_score(self) -> Optional[float]:
+        """Mean of the per-question scores, over graded questions only."""
+        scores = [s for s in (self.score_for(t.index) for t in self.tests) if s is not None]
+        if not scores:
+            return None
+        return sum(scores) / len(scores)
+
+
+@dataclass(frozen=True)
+class PluginInfo:
+    """What the server reports about a discovered plugin."""
+
+    name: str
+    slug: str
+    version: str
+    description: str
+    path: str
+    enabled: bool
+    hooks: List[str] = field(default_factory=list)
+    error: Optional[str] = None