refactor: replace fragile StackTrace RegExp parsing with package:stack_trace

@Mastersam07 is already working on this.

Since Jul 20, 2026.

[authored by Randal, assisted by Gemini]

## Problem
In `packages/kaisel_core/lib/src/kaisel_router.dart`, the helper function `kaiselOriginFrames` captures and parses the stringified representation of a `StackTrace` using a regular expression (`_frameLocation`) to resolve file paths, lines, and columns for DevTools support:

https://github.com/Mastersam07/kaisel/blob/dev/packages/kaisel_core/lib/src/kaisel_router.dart#L38-L58

Relying on manual RegExp parsing of `StackTrace.toString()` is highly fragile:
- Stack trace string formats are not guaranteed stable by the Dart SDK.
- The format differs significantly depending on the platform/compiler (Dart VM vs. JS vs. WebAssembly).
- Any updates to the compiler output or SDK changes can silently break DevTools frame location resolution.

## Proposed Solution
Migrate stack trace processing to the official, Dart-team-maintained [`package:stack_trace`](https://pub.dev/packages/stack_trace) which is built precisely to parse, normalize, and format stack traces reliably across VM and web platforms.

### Proposed Implementation:
1. Add `stack_trace` as a dependency in `packages/kaisel_core/pubspec.yaml`.
2. Refactor `kaiselOriginFrames` to construct a `Trace` and filter/map its frames:

```dart
import 'package:stack_trace/stack_trace.dart';

List kaiselOriginFrames(StackTrace? trace, {int limit = 5}) {
if (trace == null) return const [];

final frames = [];
final parsedTrace = Trace.from(trace);

for (final frame in parsedTrace.frames) {
final uriStr = frame.uri.toString();

// Filter out framework and SDK frames
if (uriStr.startsWith('dart:') ||
uriStr.startsWith('package:kaisel/') ||
uriStr.startsWith('package:kaisel_core/') ||
uriStr.startsWith('package:flutter/')) {
continue;
}

frames.add(
KaiselOriginFrame(
display: frame.toString(),
uri: uriStr,
line: frame.line,
column: frame.column,
),
);

if (frames.length >= limit) break;
}
return frames;
}
```