fix(app): detect session-not-found across legacy error shapes

[CannonRS]

Issue for this PR

Closes #48012

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

isSessionNotFoundError and isLocalSessionNotFoundError now also recognise
session-not-found errors that arrive through other serialisation shapes, not just
the exact V1 tagged form:

• string errors whose text contains the not-found message;
• objects with name: "NotFoundError" whose data.message equals the message;
• any serialised object whose message includes the not-found text.

The existing exact-shape checks (Error.message ===, _tag === "SessionNotFoundError")
are preserved, so current behaviour is unchanged where it already worked.

How did you verify your code works?

• bun typecheck in packages/app: clean.
• The change is a pure widening of the two predicate functions; no call-site
  changes. (A focused test for the new shapes can be added if the maintainer
  wants one; none is included to keep the diff minimal.)

Screenshots / recordings

N/A — not a UI change.

Fork

• Source fork: https://github.com/mQorva/OpenCode
• Diff against this fork's dev: mQorva/OpenCode@dev...detect-session-errors

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR