doc: restructure README to explain the return-over-throw paradigm

- Add "The Problem with try/catch" section explaining why catch(e)
  yields unknown and throw cannot express errors in type signatures
- Add "The Idea: Return Errors, Don't Throw Them" section introducing
  the return-value approach with a findUser example
- Replace mathematical examples with a login example (USER_NOT_FOUND,
  ACCOUNT_LOCKED, WRONG_PASSWORD) to make typed cause more relatable
- Use early return pattern instead of if/else in caller examples
- Convert API property list to a table with Enumerable column
- Move Features section below the problem/solution narrative

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: nakanoasaservice

README.md

@@ -61,10 +61,11 @@ if (result instanceof Error) {
   // result is TaggedError<"USER_NOT_FOUND"> — fully typed
   console.error(result.message);
   console.error("Searched for id:", result.cause.id); // typed as string
-} else {
-  // result is User here
-  console.log(result.name);
+  return;
 }
+
+// result is User here
+console.log(result.name);
 ```
 
 No `try/catch`. No type casting. No guessing.
@@ -126,10 +127,11 @@ if (result instanceof Error) {
       console.error(`${result.cause.attemptsRemaining} attempts remaining`);
       break;
   }
-} else {
-  // result is typed as { userId: string; token: string }
-  console.log("Logged in:", result.userId);
+  return;
 }
+
+// result is typed as { userId: string; token: string }
+console.log("Logged in:", result.userId);
 ```
 
 TypeScript infers the union return type automatically. If you forget to handle