Add sub-issues, issue types, projects, and issue fields guidance to github-issues skill (#884)

* Add issue fields, issue types, and list_issue_types to github-issues skill

- Add list_issue_types to available MCP tools table
- Add type parameter to optional parameters with guidance
- Expand issue types section: MCP tools (preferred) + GraphQL (advanced)
- Document org-level type discovery, create/update with type, GraphQL mutations
- Add issue fields section: discover, read, set via GraphQL
- Note required GraphQL-Features headers (issue_fields, issue_types)
- Update skill description to mention fields, types, dates, priority

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Add Projects V2 guidance to github-issues skill

Include MCP tools (projects_list, projects_get, projects_write) and
GraphQL examples for project item management.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Add sub-issues section, move issue fields to end with preview note

- Add Sub-Issues and Parent Issues section (MCP, REST, GraphQL)
- Add issue_read tool to MCP tools table
- Move Issue Fields to last section with private preview callout
- Link to community discussion for requesting access

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Prefer issue types over labels for categorization

Update guidance and examples to use type parameter (Bug, Feature)
instead of equivalent labels when issue types are available.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Prefer issue fields over project fields for metadata

Issue fields live on the issue and travel across projects.
Project fields are scoped to a single project.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Add issue dependencies (blocked by/blocking) section

Covers REST endpoints (list, add, remove) and GraphQL
(blockedBy, blocking, issueDependenciesSummary, mutations).
Also documents tracked issues read-only fields.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Add project discovery workflow for progress reports

Teach agents how to find projects by name, discover fields
and iterations, paginate items, and build status breakdowns.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Generate updated skill listing after SKILL.md changes

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Split skill into reference files per reviewer feedback

Move sub-issues, dependencies, issue types, projects, and issue fields
into separate references/ files. Main SKILL.md now contains core MCP
workflow and a capability table pointing to each reference. This way
the agent only loads the knowledge it needs for the specific task.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

skills/github-issues/references/dependencies.md

@@ -0,0 +1,71 @@
+# Issue Dependencies (Blocked By / Blocking)
+
+Dependencies let you mark that an issue is blocked by another issue. This creates a formal dependency relationship visible in the UI and trackable via API. No MCP tools exist for dependencies; use REST or GraphQL directly.
+
+## Using REST API
+
+**List issues blocking this issue:**
+```
+GET /repos/{owner}/{repo}/issues/{issue_number}/dependencies/blocked_by
+```
+
+**Add a blocking dependency:**
+```
+POST /repos/{owner}/{repo}/issues/{issue_number}/dependencies/blocked_by
+Body: { "issue_id": 12345 }
+```
+
+The `issue_id` is the numeric issue **ID** (not the issue number).
+
+**Remove a blocking dependency:**
+```
+DELETE /repos/{owner}/{repo}/issues/{issue_number}/dependencies/blocked_by/{issue_id}
+```
+
+## Using GraphQL
+
+**Read dependencies:**
+```graphql
+{
+  repository(owner: "OWNER", name: "REPO") {
+    issue(number: 123) {
+      blockedBy(first: 10) { nodes { number title state } }
+      blocking(first: 10) { nodes { number title state } }
+      issueDependenciesSummary { blockedBy blocking totalBlockedBy totalBlocking }
+    }
+  }
+}
+```
+
+**Add a dependency:**
+```graphql
+mutation {
+  addBlockedBy(input: {
+    issueId: "BLOCKED_ISSUE_NODE_ID"
+    blockingIssueId: "BLOCKING_ISSUE_NODE_ID"
+  }) {
+    blockedByIssue { number title }
+  }
+}
+```
+
+**Remove a dependency:**
+```graphql
+mutation {
+  removeBlockedBy(input: {
+    issueId: "BLOCKED_ISSUE_NODE_ID"
+    blockingIssueId: "BLOCKING_ISSUE_NODE_ID"
+  }) {
+    blockedByIssue { number title }
+  }
+}
+```
+
+## Tracked issues (read-only)
+
+Task-list tracking relationships are available via GraphQL as read-only fields:
+
+- `trackedIssues(first: N)` - issues tracked in this issue's task list
+- `trackedInIssues(first: N)` - issues whose task lists reference this issue
+
+These are set automatically when issues are referenced in task lists (`- [ ] #123`). There are no mutations to manage them.