fix(edge): respect handle.style left/top offset when computing edge endpoints

[pshoukry]

Summary

Problem: Adding multiple handles on the same side ( example: conditional with more than 3 / 4 options like a case ) is impossible since each side positions its handle at a 50% marker.

Solution: Allow adding multiple handles and distributing them evenly on the side.

When a handle carries a left (top/bottom handles) or top (left/right handles) percentage in its style map, the handle element is rendered at that visual offset by the browser — but the SVG edge endpoint was still computed from the centre of the side. Result: the edge line doesn't meet the handle circle, leaving a visible gap on branching nodes that spread their source handles (e.g. Condition / Switch / ForEach patterns where `true` and `false` handles sit at 25% and 75% of the bottom edge).

`LiveFlow.Handle` already exposes a public `:style` field intended for "Custom inline styles" — this change makes edge rendering consistent with that field instead of silently ignoring it.

Behaviour

• Handle on `:top` or `:bottom` with `style: %{"left" => "25%"}` → edge endpoint x = `node.x + node.width * 0.25`.
• Handle on `:left` or `:right` with `style: %{"top" => "20%"}` → edge endpoint y = `node.y + node.height * 0.20`.
• Handle with no style, empty style, or a non-parseable value → falls back to the previous centred behaviour.
• Atom keys (`%{left: "25%"}`) are also accepted alongside string keys.

Test plan

Five new component tests in `test/live_flow/components/edge_test.exs` covering:

• Source handle on `:bottom` with `style.left = "25%"` on a 200px-wide node at x=0 → edge starts at x=50.
• Source handle on `:bottom` with `style.left = "75%"` on a 200px-wide node at x=100 → edge starts at x=250.
• Source handle on `:bottom` with empty style → edge starts at x=100 (centre, pre-existing behaviour).
• Source handle on `:bottom` with `style.left = "garbage"` → falls back to centre.
• Source handle on `:right` with `style.top = "20%"` on a 100px-tall node → edge starts at y=20.

Full suite: 194 tests, 0 failures.