Link #123 issue and pull request references in chat (#8636)

* feat(app): link #123 issue and pull request references in Markdown

Agents cite issues and pull requests by number; reading one meant looking
up the URL by hand. Markdown in a workspace now links forge shorthand
against the workspace's origin remote: `#N`, GitLab and Gitea `!N`, and
cross-repository `owner/repo#N` on the same host.

Each forge's URL grammar declares which sigil maps to which path, so the
syntax stays per forge: GitHub has no `!`, and its `#` targets /issues/,
which GitHub redirects to the pull request. Recognition goes through the
Markdown engine's text link regex so code spans, fences and authored links
stay plain without a second Markdown parse while streaming. The reference
alternative sits before path recognition so `group/project#12` is not read
as a file path.

* fix(app): keep http:// for self-hosted forge web links

A self-hosted forge cloned over http:// serves its web UI over http on
the same origin. Forcing https made reference, blob and tree links fail
against an HTTP-only port. Cloud hosts and SSH remotes stay on https.

packages/app/src/git/forges/gitlab.ts

@@ -166,8 +166,8 @@ export const gitlabForgeLogic = {
     lineAnchor: gitlabLineAnchor,
     changeRequestChecksSuffix: "/pipelines",
     referencePaths: [
-      { kind: "change_request", infix: "/-/merge_requests/" },
-      { kind: "issue", infix: "/-/issues/" },
+      { kind: "change_request", infix: "/-/merge_requests/", sigil: "!" },
+      { kind: "issue", infix: "/-/issues/", sigil: "#" },
     ],
   },
   facts: defineForgeFacts({