feat(KB-144): add mobile-safe planning mode text inputs

- Set planning mode text inputs to 16px font size to prevent iOS auto-zoom on focus

- Update TaskDetailModal component with mobile-safe input styling

- Add CSS styles for mobile-safe planning mode inputs

- Add unit tests for mobile planning input font size behavior

- Document mobile-safe planning mode input behavior and rationale

packages/dashboard/app/__tests__/mobile-planning-input-font-size.test.ts

@@ -0,0 +1,70 @@
+import { describe, it, expect } from "vitest";
+import { readFileSync } from "fs";
+import { resolve } from "path";
+
+const css = readFileSync(
+  resolve(__dirname, "../styles.css"),
+  "utf-8",
+);
+
+describe("mobile planning input font size CSS", () => {
+  describe("base (desktop) styles", () => {
+    it("planning-textarea has desktop font-size below 16px", () => {
+      // Extract the .planning-textarea rule
+      const textareaMatch = css.match(/\.planning-textarea\s*\{[^}]*\}/);
+      expect(textareaMatch).not.toBeNull();
+
+      // Should have 14px font-size on desktop
+      expect(textareaMatch![0]).toContain("font-size: 14px");
+    });
+  });
+
+  describe("mobile @media (max-width: 768px)", () => {
+    it("contains mobile font-size override for planning-textarea", () => {
+      // Find the mobile planning modal media query
+      const planningModalMediaMatch = css.match(
+        /@media\s*\([^)]*max-width:\s*768px[^)]*\)\s*\{[^}]*\.planning-modal/s,
+      );
+      expect(planningModalMediaMatch).not.toBeNull();
+
+      // Extract the mobile planning modal block
+      const mediaStart = css.search(
+        /@media\s*\([^)]*max-width:\s*768px[^)]*\)\s*\{[^}]*\.planning-modal/s,
+      );
+      const afterMedia = css.slice(mediaStart);
+
+      // Find the end of this specific media block (next @media or end of string)
+      const nextMedia = afterMedia.slice(1).search(/@media/);
+      const mobileBlock = nextMedia > 0 ? afterMedia.slice(0, nextMedia + 1) : afterMedia;
+
+      // Should contain .planning-textarea with 16px font-size
+      expect(mobileBlock).toContain(".planning-textarea");
+      expect(mobileBlock).toContain("font-size: 16px");
+    });
+
+    it("only targets planning mode textareas, not all textareas globally", () => {
+      // The selector should specifically target .planning-textarea
+      // not a global textarea selector that would affect all textareas
+      const globalTextareaPattern = /@media[^{]*max-width[^}]*\{[^}]*textarea\s*\{[^}]*font-size:\s*16px/s;
+      expect(css).not.toMatch(globalTextareaPattern);
+    });
+
+    it("planning-textarea font-size is within the mobile media query", () => {
+      // Find .planning-textarea font-size: 16px
+      const planningTextarea16pxMatch = css.match(
+        /\.planning-textarea\s*\{[^}]*font-size:\s*16px[^}]*\}/,
+      );
+      expect(planningTextarea16pxMatch).not.toBeNull();
+
+      // Check it appears after a mobile media query
+      const matchIndex = css.indexOf(planningTextarea16pxMatch![0]);
+      const cssBeforeMatch = css.slice(0, matchIndex);
+      const lastMediaQuery = cssBeforeMatch.lastIndexOf("@media");
+      expect(lastMediaQuery).toBeGreaterThanOrEqual(0);
+
+      // Verify the last media query before our rule is a mobile one
+      const mediaQueryText = cssBeforeMatch.slice(lastMediaQuery, lastMediaQuery + 50);
+      expect(mediaQueryText).toContain("max-width: 768px");
+    });
+  });
+});