align README outbound examples with egress docs

[iMagdy]

What

Align README.md with docs/egress.md on how the three static outbound accessors are set:
by assignment after the class declaration, not as static class fields.

Fixes the documentation half of #247.

Why

outbound, outboundByHost and outboundHandlers are declared as static accessor pairs
(dist/lib/container.d.ts:50-55), and their setters are the only writers of the handler
registry. Under useDefineForClassFields semantics — the default for target: ES2022 and
above — a static outbound = … class field is installed with [[DefineOwnProperty]]. That
creates an own property which shadows the inherited setter instead of invoking it, so the
handler is never registered and every outbound request fails closed with
520 Origin is disallowed. No error, no warning, and MyContainer.outbound still reads back
the function you assigned — it is just the own property, not a registration.

The repo already documents this correctly elsewhere. docs/egress.md uses the assignment
form in all six of its examples (lines 150, 165, 177, 310, 316, 322):

MyContainer.outboundByHost = { ... };

while README.md uses the class-field form in all six of its own (lines 311, 315, 319, 479,
485, 491). This PR makes the README match the egress docs; it does not introduce a new
convention.

All three accessors are affected identically, not just outbound.

Changes

• Reference list: show the three as assignments, and add a note explaining why the class-field
  form does not register.
• TypeScript example: move the three static blocks out of the class body into assignments
  after the declaration.

Instance properties in the same example (allowedHosts, deniedHosts, interceptHttps,
enableInternet, defaultPort) are plain properties rather than accessors, so they are
correct as class fields and are left unchanged.

Docs-only — no changeset, no behaviour change.

[iMagdy]

Quick update on scope: this PR now covers all three static outbound accessors — outbound, outboundByHost, and outboundHandlers — converting every README example to the assignment-after-class form consistent with docs/egress.md, plus a caution note (with a #247 reference) explaining why the class-field form never registers under ES2022+ (useDefineForClassFields).

#247 now documents a second production incident on top of the original fail-closed one: a fail-open variant where static outboundByHost = … with enableInternet = true silently forwards requests meant for a virtual host to the public internet — wrangler tail shows Ok, no diagnostic anywhere.

Happy to go further if preferred — I'd be glad to implement either:

1. A startup warning/throw when a class has an own outbound/outboundByHost/outboundHandlers property but no registry entry under its name (would have turned both incidents into a one-line diagnosis), or
2. Resolving handlers from the class's own static properties (or snapshotting them in the constructor), which covers both accessor forms at once.

(Also worth noting separately: examples/egress-interception/src/index.ts still uses the class-field form — out of scope for this docs PR, but it would reproduce the bug as-is.)