docs: update all docs to reflect v1 live state

- template_auto_generated.wikitext: generated_at → commit parameter
- SCHEMA.md: same banner fix; clarify that frontmatter-less files are
  silently skipped, not errors
- pipelines/songs/README.md: full rewrite — v1 live status, self-
  contained workflow pattern, correct env table, modes, one-off setup
  marked done, full decisions log
- README.md: architecture reflects actual pattern (no workflow_call),
  URL_TO_GITEA variable added, setup checklist marked complete, host
  network mode documented

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

pipelines/songs/SCHEMA.md

@@ -94,7 +94,7 @@ For each `.md` with `wiki.publish: true` and not under `wip/`:
 3. Replace `[[PLACEHOLDER]]` markers with safe tokens. *(Deferred v1; no-op until siblings are implemented.)*
 4. Pipe the body through `pandoc -f markdown -t mediawiki`.
 5. Re-substitute sibling tokens with resolved `[[Page|Display]]` wikilinks. *(Deferred v1.)*
-6. Prepend the auto-generated banner: `{{Auto-generated|source=<source URL>|generated_at=<ISO timestamp>}}`.
+6. Prepend the auto-generated banner: `{{Auto-generated|source=<source URL>|commit=<sha>}}`.
 7. Append the album category: `[[Category:<album>]]`.
 8. Read the current wiki page content via the MediaWiki API; if identical to the generated output, skip the write (idempotency — keeps the wiki history clean).
 9. Otherwise, write the page with an edit summary referencing the source commit.
@@ -164,14 +164,12 @@ wiki:
 
 ## Validation errors the renderer must produce
 
-The pipeline fails fast and loud on the following:
+Files without a `wiki.publish: true` frontmatter field are silently skipped — no error. The pipeline fails fast and loud only on files that are opted in (`wiki.publish: true`) with invalid data:
 
-- Missing or unparseable frontmatter block
-- Missing required field (`title`, `album`, `wiki.publish`)
-- `title` is empty or whitespace-only
-- `wiki.publish` is not a boolean
+- Missing required field (`title` or `album`) on a file with `wiki.publish: true`
+- `wiki.publish` present but not a boolean
 - `release_date` (if present) does not parse as YYYY-MM-DD
 - `siblings` (if present) references a file that doesn't exist
-- Two source files declare the same `title` (page-name collision)
+- Two publishable source files declare the same `title` (page-name collision)
 
 Validation runs before any wiki API calls. A failed validation aborts the run with a non-zero exit and leaves the wiki untouched.