feat(ipuaro): add impact score to initial context

Add High Impact Files section to initial context showing which files
are most critical based on percentage of codebase that depends on them.

Changes:
- Add impactScore field to FileMeta (0-100)
- Add calculateImpactScore() helper function
- Update MetaAnalyzer to compute impact scores
- Add formatHighImpactFiles() to prompts.ts
- Add includeHighImpactFiles config option (default: true)
- 28 new tests (1826 total)

packages/ipuaro/tests/unit/domain/value-objects/FileMeta.test.ts

@@ -1,5 +1,9 @@
 import { describe, it, expect } from "vitest"
-import { createFileMeta, isHubFile } from "../../../../src/domain/value-objects/FileMeta.js"
+import {
+    calculateImpactScore,
+    createFileMeta,
+    isHubFile,
+} from "../../../../src/domain/value-objects/FileMeta.js"
 
 describe("FileMeta", () => {
     describe("createFileMeta", () => {
@@ -15,6 +19,7 @@ describe("FileMeta", () => {
             expect(meta.isHub).toBe(false)
             expect(meta.isEntryPoint).toBe(false)
             expect(meta.fileType).toBe("unknown")
+            expect(meta.impactScore).toBe(0)
         })
 
         it("should merge partial values", () => {
@@ -42,4 +47,51 @@ describe("FileMeta", () => {
             expect(isHubFile(0)).toBe(false)
         })
     })
+
+    describe("calculateImpactScore", () => {
+        it("should return 0 for file with 0 dependents", () => {
+            expect(calculateImpactScore(0, 10)).toBe(0)
+        })
+
+        it("should return 0 when totalFiles is 0", () => {
+            expect(calculateImpactScore(5, 0)).toBe(0)
+        })
+
+        it("should return 0 when totalFiles is 1", () => {
+            expect(calculateImpactScore(0, 1)).toBe(0)
+        })
+
+        it("should calculate correct percentage", () => {
+            // 5 dependents out of 10 files (excluding itself = 9 possible)
+            // 5/9 * 100 = 55.56 → rounded to 56
+            expect(calculateImpactScore(5, 10)).toBe(56)
+        })
+
+        it("should return 100 when all other files depend on it", () => {
+            // 9 dependents out of 10 files (9 possible dependents)
+            expect(calculateImpactScore(9, 10)).toBe(100)
+        })
+
+        it("should cap at 100", () => {
+            // Edge case: more dependents than possible (shouldn't happen normally)
+            expect(calculateImpactScore(20, 10)).toBe(100)
+        })
+
+        it("should round the percentage", () => {
+            // 1 dependent out of 3 files (2 possible)
+            // 1/2 * 100 = 50
+            expect(calculateImpactScore(1, 3)).toBe(50)
+        })
+
+        it("should calculate impact for small projects", () => {
+            // 1 dependent out of 2 files (1 possible)
+            expect(calculateImpactScore(1, 2)).toBe(100)
+        })
+
+        it("should calculate impact for larger projects", () => {
+            // 50 dependents out of 100 files (99 possible)
+            // 50/99 * 100 = 50.51 → rounded to 51
+            expect(calculateImpactScore(50, 100)).toBe(51)
+        })
+    })
 })