chore: fix Hex package metadata so the package can be published

[Taure]

Prep for publishing rebar3_nova to Hex.

The licence problem

src/rebar3_nova.app.src declared:

{licenses, ["Apache 2.0"]}

That is not an SPDX identifier, so Hex does not recognise it as the Apache licence. The correct id is Apache-2.0 — which nova itself already uses.

The LICENSE file was already fine: complete Apache 2.0 text with the copyright line filled in (Copyright 2020, Daniel Widgren), and it is included in the package tarball. No change needed there.

Also fixed

• {links, []} was empty — now points at the GitHub repo, so the package page has a source link.
• {description, "A rebar plugin"} was a placeholder — this is the one-line blurb shown in Hex search results, so it now describes what the plugin actually does.

{vsn, git} is untouched; version still comes from the git tag.

Verified

rebar3 hex build succeeds and the resulting metadata.config carries:

{<<"licenses">>,[<<"Apache-2.0">>]}.
{<<"links">>,[{<<"GitHub">>,<<"https://github.com/novaframework/rebar3_nova">>}]}.
{<<"description">>,<<"Rebar3 plugin for scaffolding and managing Nova framework projects">>}.
{<<"version">>,<<"0.13.1">>}.

LICENSE is present in the packaged files list.

fmt --check, xref, ct (27/27) all pass.

[Taure]

Second commit added, because the licence was not the only thing blocking a usable publish.

rebar3_nova is already on Hex and the live package page currently shows the broken metadata this PR fixes:

{"description":"A rebar plugin","licenses":["Apache 2.0"],"links":{}}

While confirming that, I found a harder blocker. rebar.config leaves nova unversioned, so rebar3 hex build derives the published requirement from rebar.lock - which still pinned nova 0.10.2. That publishes as ~>0.10.2 (>= 0.10.2, < 0.11.0), while nova on Hex is at 0.15.3. Anyone on current nova would get a resolution conflict and simply could not install the plugin.

Did a full clean relock rather than a targeted upgrade, per the transitive-skew rule:

dep	before	after
nova	0.10.2	0.15.3
cowlib	2.13.0	2.19.0
ranch	1.8.0	2.2.0
jhn_stdlib	5.1.0	5.11.2
routing_tree	1.0.9	1.0.11
thoas	1.2.0	1.2.1

uuid_erl, quickrand and pmod_transform drop out - nova no longer pulls them.

Smoke-tested against the new lock: compile clean, xref clean (so the plugin's calls into the nova API still resolve across the 0.10 -> 0.15 jump), ct 27/27.

Also worth noting for whenever you publish: the last Hex release is 0.8.0 while the repo is at v0.13.1.