refactor(integrations): split issue-tracker clients under the max-lines budget (#14704)

The GitLab, GitHub, Jira and Linear integration modules, their two IPC
registrars, and the shared GitHub project types each carried a file-level
`eslint-disable max-lines` and ran 351-614 counted lines against a 300-line
budget. AGENTS.md calls for splitting rather than suppressing, and
config/max-lines-baseline.txt is a shrink-only ratchet, so this removes all
eight suppressions and prunes their entries (341 -> 333).

Pure move, no behavior change. Each client is cut along the seam it already
had: per-operation modules for the issue APIs (create / update / comment /
field options), and for Jira the request queue, site credential store,
authenticated request, and site identity. The two IPC registrars keep their own
handlers and delegate the rest to per-domain sub-registrars, so they remain
real entry points rather than re-export shims.

The IPC surface is proved intact rather than assumed: comparing (method,
channel) multisets between HEAD and the split gives 52 registrations across 52
distinct channels on both sides.

Provider-neutrality is preserved -- GitLab and GitHub keep separate, parallel
module layouts rather than being merged behind a shared abstraction.

Verified: oxlint clean, ratchet passes, typecheck clean, full unit suite green
(the one remaining failure is a pre-existing load flake in an untouched file,
green when re-run serially), no new runtime import cycles among 744 modules,
and no lint suppression added anywhere.

src/main/gitlab/project-path-encoding.ts

@@ -0,0 +1,6 @@
+// Why: GitLab REST API addresses projects by URL-encoded path. Centralize
+// the encoding so a future call site can't forget it (the slash escapes
+// are easy to miss).
+export function encodedProject(projectPath: string): string {
+  return encodeURIComponent(projectPath)
+}