fix(gitea-releases): restore the prerelease imperative to the create path

The retrofit left only a descriptive sentence on the loaded path — "Gitea
never infers a prerelease from a -beta/-rc tag name" — and moved the
imperative into references/conventions.md behind a trigger listing semver
naming, release-notes sourcing and release-to-tag relationships. Draft and
prerelease are not in that list, and "cut a v2.0.0-beta.1" is exactly the
request where the caller does not raise the topic, so the rule was
unreachable from the flow that needs it.

Severity comes from the repair path: the MCP surface has create, get,
get_latest, list and delete only — there is no update or edit tool. A
release published without is_pre_release can only be corrected by
delete_release plus a fresh create, and get_latest_release points
consumers at the beta meanwhile. Neither SKILL.md nor call-signatures.md
said so anywhere.

The flags are now set explicitly on every create, the missing update tool
and its delete-and-recreate consequence are stated in the body, and the
semver pass-through rule stranded behind the same trigger is promoted
alongside it. call-signatures.md now cites the deployed tool description
as direct evidence that get_latest_release excludes drafts, while keeping
the prerelease half hedged — that remains unconfirmed.

Verified live against gitea-mcp v1.7.0, read-only calls.

Refs #99

plugins/gitea/skills/gitea-releases/references/conventions.md

@@ -33,6 +33,13 @@ commonly used to signal a prerelease to humans. When a user asks to "cut a beta"
 release candidate," set `is_pre_release: true` explicitly in the same call rather than relying on
 the tag string to carry that meaning.
 
+Getting this wrong is not cheaply repairable. The gitea-mcp release surface is `create_release`,
+`get_release`, `get_latest_release`, `list_releases` and `delete_release` — there is **no update or
+edit tool**, so a published release's flags cannot be corrected in place. The only remedy is
+`delete_release` plus a fresh `create_release`, a destructive round trip; meanwhile a beta published
+without `is_pre_release` is the release `get_latest_release` returns. Set the flags in the create
+call.
+
 Note the input/output naming mismatch: the input param is `is_draft`, but the release object
 returned by the API uses `draft` (and `prerelease`) as the field names. `draft` is never a valid
 input key — passing `draft: true` to `create_release` is silently ignored rather than erroring.