feat: add v0.3 normalised comparison reasoning

Add explicit reasoning guidance for normalising counts by exposure/denominator,
distinguishing total count from rate, and avoiding correlation-as-causation errors.

Changes:
- prompts/reconstruct-v0.3.md: new prompt with normalisation discipline
- lib/reconstruction/prompt.js: v0.3 loader + env var override support
- lib/analysis.js: defer DEFAULT_PROMPT_VERSION to prompt module (defaults to v0.3)
- PROMPT_VERSIONS extended to [v0.1, v0.2, v0.3]
- tests/v03-reasoning.test.js: 34 focused tests covering prompt loading, schema validation, guidance completeness, and target scenario fixture
- playwright.config.js + tests/smoke.test.js: minimal UI smoke test for browser rendering
- package.json: add @playwright/test as devDependency

Default switches to v0.3; v0.2 selectable via promptVersion or RECONSTRUCTION_PROMPT_VERSION env var.

lib/reconstruction/prompt.js

@@ -7,7 +7,14 @@ const __dirname = dirname(__filename);
 const PROMPTS_DIR = join(__dirname, "../../prompts");
 
 /** Available prompt versions */
-export const PROMPT_VERSIONS = ["v0.1", "v0.2"];
+export const PROMPT_VERSIONS = ["v0.1", "v0.2", "v0.3"];
+
+/** Default prompt version (override via RECONSTRUCTION_PROMPT_VERSION env var) */
+const defaultVersionFromEnv = process.env.RECONSTRUCTION_PROMPT_VERSION;
+export const DEFAULT_PROMPT_VERSION =
+  defaultVersionFromEnv && PROMPT_VERSIONS.includes(defaultVersionFromEnv)
+    ? defaultVersionFromEnv
+    : "v0.3";
 
 /** Build a v0.1 (extraction-only) prompt inline for backward compatibility */
 function buildV1Prompt(scenario) {
@@ -56,20 +63,37 @@ async function buildV2Prompt(scenario) {
   }
 }
 
+/** Load a versioned prompt from disk and substitute {{SCENARIO}} */
+async function buildV3Prompt(scenario) {
+  try {
+    const content = await fs.readFile(
+      join(PROMPTS_DIR, "reconstruct-v0.3.md"),
+      "utf-8",
+    );
+    return content.replace("{{SCENARIO}}", scenario);
+  } catch {
+    // Fall back to v0.2 prompt if v0.3 file is missing
+    return buildV2Prompt(scenario);
+  }
+}
+
 /**
  * Build an analysis prompt for the given version.
- * @param {"v0.1" | "v0.2"} [version="v0.2"]
+ * @param {"v0.1" | "v0.2" | "v0.3"} [version="v0.3"]
  * @returns {Promise<{prompt: string, version: string}>}
  */
-export async function buildPrompt(scenario, version = "v0.2") {
+export async function buildPrompt(scenario, version = "v0.3") {
   let prompt;
   switch (version) {
     case "v0.1":
       prompt = buildV1Prompt(scenario);
       break;
-    default: // v0.2
+    case "v0.2":
       prompt = await buildV2Prompt(scenario);
       break;
+    default: // v0.3
+      prompt = await buildV3Prompt(scenario);
+      break;
   }
 
   const strongJsonHint =