v0.1.44

Make serving a package to the browser a mechanism

comet was one special case. chronos was a second, and I wrote it by
copying the first. atom would have been a third copy of the same
fourteen lines, which is the point at which a branch per package stops
being a shortcut and starts being the design.

config.browserPackages takes bare specifiers; DEFAULT_BROWSER_PACKAGES
keeps comet and chronos automatic, since aurora generates code that
imports them. Adding atom is now one line in config/aurora.ts instead
of ~200 across four files and a release.

What the mechanism knows, which the copies each had to be told: a
package needs its dist on a URL, its wasm sibling too WHEN it has one
-- probed, not declared, because a package gains or loses a wasm build
between releases and a list here would be one more thing to keep in
step with packages aurora does not own -- and an importmap entry
pointing INTO dist so a relative ../wasm/ lands on the sibling route
rather than climbing out of the mount. Never the package root, which
would answer both and also publish index.*.node.

Two packages resolving to the same mount now throw instead of serving
one of them unreachably, decided by registration order.

BEHAVIOUR CHANGE: comet's importmap entry moves from
/__assets/comet/index.js to /__assets/comet/dist/index.js, uniform with
every other served package. The importmap is regenerated on each render
and no consumer writes that URL, so nothing carries it forward.

Net 69 insertions against 106 deletions in src/.

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Changes since v0.1.43.