v0.1: Grav-only repo + CI lint + branch-preview architecture

Pipeline fully retired: src/, contract-inputs/, service-csv/ deleted;
their content is fully superseded by grav/user/pages (verified section
by section). New: gitea actions lint workflow (markdownlint + typos
blocking, vale prose + lychee links advisory), lint configs, README
documents the branch/PR model, docs/branch-previews.md is the LAMP +
wildcard + Git Sync runbook for <branch>.contract.knownelement.com.
Blocking checks verified green before push (pinned containers).

Ticket: https://projects.knownelement.com/issues/924

.markdownlint.yaml

@@ -0,0 +1,8 @@
+# Contract content is Grav markdown with frontmatter and legal prose.
+MD013: false  # line length — legal sentences are long
+MD041: false  # first-line heading — Grav pages start with frontmatter
+MD033: false  # inline HTML — allowed for embeds
+MD036: false  # no-emphasis-as-heading — legal drafting style
+MD025: false  # services page is a concatenation of catalog sections, each with an H1
+MD024:
+  siblings_only: true  # repeated headings across sections are fine