docs: update ecosystem inventory and syntax pointers

[seabbs-bot]

This is entirely from an agent so do not review until I have pinged for review as I will do a first pass

Sam asked for this org-site update after several packages moved:
DistributionsInference.jl became the inference home, ComposedDistributions
gained uncertain(tree, ...)/update(tree, table) and leaf-level
truncated()/censored() support, and a couple of docs links had drifted
from what is actually deployed.

Ecosystem inventory

• Add DistributionsInference.jl to packages/index.qmd. It has no GitHub
  Pages deployment yet (the Pages API 404s, confirmed just now), so it links
  its GitHub repo rather than a docs subdomain, per the current convention
  for undeployed packages.
• Refresh LoweredDistributions.jl's description: it undersold current scope
  ("nothing to install yet") when it already lowers a distribution or a
  whole composed event tree onto a phase-type chain or CTMC, across four
  backend extensions.
• Bump ConvolvedDistributions.jl and EpiAwareADTools.jl from experimental
  to maturing — both are now registered in General (0.2.0 and 0.1.0
  respectively, per ComposedDistributions' own NEWS.md).

Syntax examples

• The homepage and composed-distributions approach page share one hero code
  block; both now use @uncertain compose(...) with a real uncertain leaf
  (Gamma(Normal(1.2, 0.2), 3.0)) instead of a tree with nothing uncertain
  in it, matching how ComposedDistributions' own README demonstrates it.
• The approach page's prose now documents uncertain(tree; ...) as the
  promotion verb over an existing tree, the update(tree, table) /
  update(tree, chain) split, and Distributions.jl's own truncated() and
  censored() working as ordinary leaves (correcting a mislabel that
  attributed censored() to CensoredDistributions.jl rather than
  Distributions.jl itself — they are different things).
• Added LoweredDistributions.jl and DistributionsInference.jl to the
  approach page's "Where next" list, since it already discusses lowering
  and fitting without naming either package.

Link and architecture fixes

• Two remaining "GitHub Discussions" mentions in faq.qmd and
  get-involved.qmd routed to the forum instead (the earlier fix in fix: route help via the forum, not disabled Discussions #21
  only touched a different page).
• Three ConvolvedDistributions.jl links pointed at /stable/ paths that are
  not actually deployed — I checked its gh-pages branch directly and it
  only has a dev/ folder (its root index.html redirects to ./dev/,
  unlike CensoredDistributions' which redirects to ./stable/), despite
  ConvolvedDistributions being a registered package. Fixed to /dev/.
• Conversely, four CensoredDistributions.jl tutorial links pointed at
  /dev/ when /stable/ is what's actually deployed (verified all four
  paths exist under stable/getting-started/tutorials/ on its gh-pages
  branch) — fixed to /stable/.
• README's description of the site structure was stale
  (packages/_template.qmd and docs.qmd/EPIAWARE_DOCS no longer exist;
  the site now has one filterable packages/index.qmd and one filterable
  tutorials/index.qmd) — updated to match.

No stale "GitHub Discussions" mentions or extension-hosting architecture
claims remain anywhere else on the site (checked with a full-site grep).

All seven changed pages render cleanly with quarto render (rendered
individually rather than the full site, given a memory-tight shared host).

This was opened by a bot. Please ping @seabbs for any questions.

[seabbs-bot]

Independent QA: MERGE-CLEAN.

A second agent re-verified this PR independently: every syntax claim (the @uncertain macro, uncertain(tree, ...), update(tree, table)/update(tree, chain), distribution_priors/distribution_params, leaf-level truncated()/censored()) was run against a clean checkout of each package's current main, and every doc link was checked against the live gh-pages state rather than assumed from registration status. One adjacent limitation in ComposedDistributions.jl turned up during that check and is being filed separately as a CD issue rather than addressed here, since it's out of scope for the site.

@seabbs — ready for your read whenever convenient. Left as draft per your preference.

[github-actions]

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