[Change] Add backlog add (interactive issue creation)

[djm81]

Why

After implementing backlog adapters and dependency analysis (add-backlog-dependency-analysis-and-commands), teams can analyze and sync backlog items but cannot create new issues from the CLI with proper scoping, hierarchy alignment, and Definition of Ready (DoR) checks. Without a dedicated add flow, users create issues manually in GitHub/ADO and risk orphaned or misaligned items. Adding specfact backlog add enables interactive creation with AI copilot assistance: draft → review → enhance → validate (graph, DoR) → create, so new issues fit the existing backlog structure and value chain.

What Changes

• NEW: Add CLI command specfact backlog add (or alias specfact backlog add-issue) for interactive creation of backlog issues (epic, feature, story, task, bug, spike) with optional parent, title, body, and DoR validation.
• NEW: Support multiple backlog levels (epic, feature, story, task, bug, spike, custom) with configurable creation hierarchy (allowed parent types per child type) via template or backlog_config; default derived from existing type_mapping and dependency_rules.
• NEW: Extend backlog adapters with abstract method create_issue(project_id, payload) returning created item (id, key, url); implement in GitHub and ADO adapters with unified payload shape and provider-specific mapping.
• NEW: Add flow: load graph, resolve type and parent from template/hierarchy, validate parent exists and allowed type, optional DoR check (reuse backlog refine DoR; use Policy Engine [Change] Unified Policy Engine (DoR/DoD/Flow/PI) — Δ1 #176 for DoR enforcement when available), map draft to provider payload, call adapter create_issue, output created id/key/url.
• EXTEND (E5): Use Policy Engine ([Change] Unified Policy Engine (DoR/DoD/Flow/PI) — Δ1 #176) for DoR enforcement when available; provide draft patch preview before create (integrate with patch-mode-preview-apply [Change] Patch mode for backlog/spec edits (previewable, confirmable) — Δ2 #177 when available) so user can review proposed issue body/fields before creating.
• EXTEND: Template or backlog_config with optional creation_hierarchy so Scrum/SAFe/Kanban and custom hierarchies work without code changes.
• EXTEND: Documentation (agile-scrum-workflows, backlog-refinement) for backlog add workflow, interactive creation, DoR, and slash-prompt usage.

Acceptance Criteria

• Multiple backlog levels supported (epic, feature, story, task, bug, spike, custom) with configurable hierarchy (default from template; overrides from backlog_config).
• Interactive creation flow: draft → review → enhance → validate (dependencies, DoR) → create; usable by single user or team (e.g. sprint planning) and invokable via CLI or slash prompt.
• New item is validated against existing graph (parent exists, allowed type, no cycles) and DoR before create.
• Adapters expose create (e.g. create_issue); GitHub and ADO implemented; payload is unified, provider-specific mapping inside adapter.
• Spec and tests first; implementation satisfies spec and tests.
• Documentation updated for backlog add workflow and custom hierarchy.

Dependencies (E5)

• [Change] Unified Policy Engine (DoR/DoD/Flow/PI) — Δ1 #176 (Unified Policy Engine): Use Policy Engine for DoR enforcement when available.
• [Change] Patch mode for backlog/spec edits (previewable, confirmable) — Δ2 #177 (Patch Mode): Provide draft patch preview before creating issue so user can review proposed body/fields.

OpenSpec Change Proposal: add-backlog-add-interactive-issue-creation