Herald.OSS v0.2.0

Coordinated breaking-changes release. No external adopters yet — the
window for cheap breaking changes is now. The three changes below are
the kind of residue and bug fix that's expensive to land after 1.0.

Removed (breaking)

• HeraldEdition type and MinimumEdition property on
  ILogSinkProvider. Herald.OSS is a single-edition distribution
  with no runtime gate; the type and the property surface were inert
  plumbing. Sink authors that previously declared
  public HeraldEdition MinimumEdition => HeraldEdition.Community;
  remove the line. Commercial wrappers that want to keep an edition
  badge can layer it back on as their own type.
• HeraldTenant.EnsureAllowedForCurrentEdition method. The OSS
  implementation was an empty body; gate enforcement is downstream-
  only. The two call sites in HeraldRegistryInstance are removed.
• GenSource field on LogEvent, LogEventBuffer,
  LogEventFactory, DeferredLogEventFactory,
  ILogEventFactory, and the _genSource plumbing through
  StructuredLogger, DefaultLogPipelineFactory, HotPathLogger,
  and WindowedMeanLogger. The provenance gate was already absent
  from the OSS distribution; the field was inert. Downstream
  commercial wrappers that need a provenance carrier can stamp the
  value into Context["gen_source"] instead.

Changed (breaking)

• StructuredLogger.IsXxxAcceptable and
  HotPathLogger.IsXxxAcceptable are now properties, not fields.
  Source-compatible: if (logger.IsDebugAcceptable) ... keeps
  binding to the same member name. Binary-breaking for pre-compiled
  consumer assemblies that linked the field by ldfld; recompile
  against 0.2.0 to restore. The property getter is a single
  Volatile.Read so the emitted reject path stays one load plus
  branch.
• Level-only hot reload now recomputes the per-known-level accept
  booleans. A RecomputeAcceptables hook on the outer
  StructuredLogger is called from the level-only branch of
  HotReloadableLoggingBootstrap.ExecuteReload. Without this hook,
  a level-only reload that lowered the minimum left source-gen-
  emitted reject sites reading the stale field value — events at
  the newly-accepted levels were silently dropped.

Added

• Unit test IsXxxAcceptableHotReloadTests pinning the
  IsXxxAcceptable property values at construction and after a
  RecomputeAcceptables call that lowers, raises, or clears the
  minimum.

Verifying this release

• Build clean on net8 / net9 / net10
• Test suite: 184 / 185 / 185 passing (no skips)
• dotnet pack produces Herald.OSS.0.2.0.nupkg + .snupkg