Fix eight defects found offline, and unbreak the test suite

[Pimptasty]

Eight defects, each found by running the existing tests/ suite offline and writing a test for
what the code should do. Every fix has a regression test in this PR.

The suite on this branch is currently red — two errors in TestConfig. GwConfig:reload()
calls C_GuildInfo.GuildRoster() bare, while tests/TestConfig.lua asserts a fallback to the
global. The first commit restores the feature-detect so the two agree; it also protects a client
without the namespace, which raises there on the very first configuration load, before the bridge
comes up.

The rest

• GW:v: could abort the entire configuration parse. The guard
  '^%d+%.%d+%.%d+%w*$' accepts 1.2.3beta, which is not a semantic version — a pre-release needs
  the -. semver() returns nothing, tostring() then raises with no argument, and load()
  unwinds before the channel, peer and officer directives on the following lines are read. One
  mistyped character in the Guild Information panel takes a whole confederation's configuration
  down. Now validated by parsing rather than by regex.

• GwConfig:is_container() raised on every call — self:GetGuildName(), which GwConfig does
  not define. The helper is gw.GetGuildName().

• The Interface Options "Defaults" button raised. GwSettings:reset() requires an svtable,
  but GreenWallInterfaceFrame_SetDefaults calls it with none. Underneath sat a second defect:
  the body only assigned a default when the stored value was absent or invalid — a guard that
  belongs to initialize(), making reset() a no-op on any real store even when called correctly.

• API handlers registered with '*' never received anything. The dispatcher tested whether the
  sending addon was named '*', but AddMessageHandler and SendMessage both assert the addon
  against C_AddOns.GetAddOnInfo, so no real sender can be. The wildcard belongs to the
  registration, as API.md documents.

• The bridge channel was never hidden. GwChannel:join() scans GetChatWindowMessages() for
  the channel name, but that returns message group names (GUILD, SAY) — the channel list is
  GetChatWindowChannels(). Blizzard reads the two into RegisterForMessages and
  RegisterForChannels respectively, so a group name can never equal a channel name and the loop
  matches nothing. Had it matched it would have raised: ChatFrame_RemoveChannel is a deprecation
  alias for ChatFrameMixin.RemoveChannel, which takes the frame as self, and the call passed the
  frame's name.

• Hold-down timers could stop firing silently, and leaked a frame per start. GwHoldDown:start()
  created its OnUpdate frame into a bare local; nothing else referenced it, because the handler
  takes frame as a parameter rather than capturing it. A timer that stops produces no error at
  all. Created once, kept on the instance, reused.

• Three pre-release precedence defects in Lib/SemanticVersion.lua, in code that had never
  executed: a version with build metadata but no pre-release (1.0.0+20130313144700, valid per
  semver 2.0.0 §10) was rejected outright; the comparison was not antisymmetric, so
  1.0.0-alpha < 1.0.0-1 and 1.0.0-1 < 1.0.0-alpha were both true; and a shorter pre-release
  outranked a longer one, making 1.0.0-alpha rank above 1.0.0-alpha.1. TestSemanticVersion.lua
  walks the specification's own worked example.

  VERSION_MINOR goes 1 → 2, which is load-bearing rather than bookkeeping:
  LibStub:NewLibrary returns nil when oldminor >= minor, so at an unchanged minor this corrected
  copy would lose to any other add-on carrying an older copy that loaded first, and the fixes would
  ship without ever running.

Docs

gw.usage did not list mode, joindelay or refresh, so three working commands were
undiscoverable in game. README.md documented a stats command that has never existed — the slash
handler has no such branch.

Testing

All seven test files pass on this branch. luaunit is not vendored here, so:

LUA_PATH="./?.lua;./tests/?.lua;/path/to/luaunit/?.lua;;" lua tests/TestSemanticVersion.lua

The SemanticVersion tests fail 5/17 against the unfixed library and pass 17/17 with the fix.

Same change is offered against main, release/classic and release/classic-era.

[mrogaski]

Please submit each of the fixes as a separate pull request. With all eight fixes in one commit, it's difficult to isolate any regressions.