fix(gitea-labels-milestones): read exclusive per label, never infer it

SKILL.md called `exclusive` "an org-labels-only flag" and concluded that
applying a Kind/*, Priority/* or Status/* label "must replace the one
already there, not stack on it". Live `list_repo_labels` on this repo
returns `exclusive` on every REPO label: all seven Kind/* plus
Compat/Breaking are false, while Priority/*, Reviewed/* and Status/* are
true. So the field is not org-only, and the replace rule would strip a
valid Kind/* label — a destructive write from a false premise.

The nuance kept: label_write's `exclusive` parameter genuinely is
annotated org-only, so that row was schema-accurate. The error was
generalising a write-parameter restriction into a claim about where the
field exists. The row is qualified rather than deleted.

The rule is now per-label: where exclusive is true the server drops the
sibling itself, so do not pre-remove; where it is false the label is
legitimately stackable.

Also fixes the org-label fallback, which treated any list_org_labels
failure as proof the owner is a user account with no org pool and said so
was "an answer, not an error to report". Under the token scopes this skill
declares the call fails with required=[read:organization] before any
org-vs-user determination is made, so a capability gap was being reported
as an absent label. Scope errors are now distinguished and reported.

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

Refs #99

plugins/gitea/skills/gitea-labels-milestones/references/labels.md

@@ -37,7 +37,7 @@ or **org-scoped** labels — never both in one call. Pick the method family (`*_
 | `name` | string | required for create |
 | `color` | string | hex `#RRGGBB`, required for create |
 | `description` | string | optional |
-| `exclusive` | boolean | org labels only |
+| `exclusive` | boolean | accepted as a *write* param on org creates only — repo labels still carry and enforce `exclusive`, set outside this tool surface |
 | `is_archived` | boolean | repo labels only |
 
 Note: unlike `milestone_read`/`milestone_write`, `owner`/`repo`/`org` are **not** schema-required on
@@ -53,6 +53,12 @@ label_read  method: "list_repo_labels"  owner: <owner>  repo: <repo>  per_page:
 Paginate (`page: 1, 2, ...`) until the returned count is less than `per_page`. This is the only way
 to build a complete name → ID map — there is no lookup-by-name endpoint.
 
+Every returned repo label carries its own `exclusive` boolean; the field is not org-only. Verified on
+`Defame1297/holocron`: all `Priority/*`, `Reviewed/*` and `Status/*` labels are `exclusive: true`,
+while all `Kind/*` labels and `Compat/Breaking` are `exclusive: false`. Where it is `true` Gitea
+enforces one-label-per-scope server-side; where it is `false` labels in that scope stack legitimately.
+Read the field — never infer exclusivity from the `/` in a name.
+
 ## Get one label
 
 ```
@@ -65,8 +71,10 @@ There is no direct name lookup. List all repo labels (paginating if needed), sca
 case-insensitive name match, and extract `id`. Both pools can apply to one issue: if the name is
 not in `list_repo_labels`, also check `list_org_labels` before reporting it unresolved. That method
 takes `org`, not `owner`/`repo` — pass the repo's `owner` as `org`, which is what it means when the
-owner is an organisation. If that call fails, the owner is a user account, there is no org pool, and
-the miss is a real miss.
+owner is an organisation. Its failure modes are not interchangeable. `token does not have at least
+one of required scope(s), required=[read:organization]` means the org pool was never queried — report
+that missing scope rather than reporting the label unresolved. Only a not-found response means the
+owner is a user account with no org pool, making the miss a real miss.
 
 Resolution is the required first step before any label application on an issue or PR — the actual
 `add_labels`/`replace_labels`/`remove_label` call lives in `gitea-issues`/`gitea-prs` via
@@ -83,7 +91,10 @@ label_write  method: "create_repo_label"
 ```
 
 For an org label, use `method: "create_org_label"` with `org:` instead of `owner`/`repo`, and
-`exclusive: true` if the label belongs to a mutually-exclusive scope group.
+`exclusive: true` if the label belongs to a mutually-exclusive scope group. `label_write` accepts
+`exclusive` on org methods only, so a repo label's exclusivity cannot be set or cleared through this
+tool — it is set in the Gitea UI or against the REST API directly, and read back via
+`list_repo_labels`.
 
 ## Edit a label