refactor: consolidate and debloat calendar sync implementation

Merge duplicated Google/Outlook engines, background handlers, and API
layers into shared calendarSync modules to cut complexity without changing
user-facing sync behavior.

src/seqta/ui/colors/parseCssColor.test.ts

@@ -1,8 +1,4 @@
-import {
-  extractSolidColor,
-  normalizeCssColorString,
-  parseCssColor,
-} from "./parseCssColor";
+import { extractSolidColor, normalizeCssColorString } from "./parseCssColor";
 
 describe("normalizeCssColorString", () => {
   it("lowercases uppercase RGBA/RGB function names", () => {
@@ -28,19 +24,3 @@ describe("extractSolidColor", () => {
     ).toBe("rgba(201,61,0,1)");
   });
 });
-
-describe("parseCssColor", () => {
-  it("parses uppercase RGBA without throwing", () => {
-    const parsed = parseCssColor("RGBA(3, 29, 11, 0.58)");
-    expect(parsed.alpha()).toBeCloseTo(0.58, 2);
-    expect(parsed.red()).toBe(3);
-    expect(parsed.green()).toBe(29);
-    expect(parsed.blue()).toBe(11);
-  });
-
-  it("falls back when the value is not a colour", () => {
-    expect(parseCssColor("not-a-color", "#007bff").hex().toLowerCase()).toBe(
-      "#007bff",
-    );
-  });
-});

src/seqta/ui/colors/parseCssColor.ts

@@ -1,7 +1,3 @@
-import Color from "color";
-
-type ColorInstance = ReturnType<typeof Color>;
-
 /**
  * SEQTA themes and user gradients often use uppercase `RGBA()` / `RGB()`.
  * The `color` package only accepts lowercase function names.
@@ -32,34 +28,3 @@ export function extractSolidColor(value: string): string | null {
   }
   return null;
 }
-
-/** Parse a CSS colour for the `color` library; never throws. */
-export function parseCssColor(value: string, fallback = "#007bff"): ColorInstance {
-  const candidates = [
-    extractSolidColor(value),
-    normalizeCssColorString(value),
-  ].filter((candidate): candidate is string => Boolean(candidate));
-
-  for (const candidate of candidates) {
-    try {
-      return Color(candidate);
-    } catch {
-      // try next strategy
-    }
-
-    const rgbaMatch = candidate.match(
-      /rgba?\(\s*([\d.]+)\s*,\s*([\d.]+)\s*,\s*([\d.]+)(?:\s*,\s*([\d.]+))?\s*\)/i,
-    );
-    if (rgbaMatch) {
-      try {
-        const [, r, g, b, a] = rgbaMatch;
-        const rgb = Color.rgb(Number(r), Number(g), Number(b));
-        return a !== undefined ? rgb.alpha(Number(a)) : rgb;
-      } catch {
-        // fall through
-      }
-    }
-  }
-
-  return Color(fallback);
-}