feat: /gsd-ultraplan-phase [BETA] — offload plan phase to Claude Code ultraplan (#2378)

* docs: add design spec for /gsd-ultraplan-phase beta command

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

* feat: add /gsd-ultraplan-phase [BETA] command

Offloads GSD plan phase to Claude Code's ultraplan cloud infrastructure.
Plan drafts remotely while terminal stays free; browser UI for inline
comments and revisions; imports back via existing /gsd-import --from.

Intentionally isolated from /gsd-plan-phase so upstream ultraplan changes
cannot break the core planning pipeline.

Closes #2374

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

* fix: resolve 5 pre-existing test failures before PR

- ARCHITECTURE.md: update command count 75→80 and workflow count 72→77
  (stale doc counts; also incremented by new ultraplan-phase files)
- sketch.md: add TEXT_MODE plain-text fallback for AskUserQuestion (#2012)
- read-guard.test.cjs: clear CLAUDECODE env var alongside CLAUDE_SESSION_ID
  so positive-path hook tests pass when run inside a Claude Code session

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

* docs: add BETA.md with /gsd-ultraplan-phase user documentation

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

* fix: address CodeRabbit review — MD040 fence labels and sketch.md TEXT_MODE duplicate

- Add language identifiers to all unlabeled fenced blocks in
  ultraplan-phase.md and design spec (resolves MD040)
- Remove duplicate TEXT_MODE explanation from sketch.md mood_intake step
  (was identical to the banner step definition)
- Make AskUserQuestion conditional explicit in mood_intake prose

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

---------

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

docs/ARCHITECTURE.md

@@ -113,7 +113,7 @@ User-facing entry points. Each file contains YAML frontmatter (name, description
 - **Copilot:** Slash commands (`/gsd-command-name`)
 - **Antigravity:** Skills
 
-**Total commands:** 79
+**Total commands:** 80
 
 ### Workflows (`get-shit-done/workflows/*.md`)
 
@@ -124,7 +124,7 @@ Orchestration logic that commands reference. Contains the step-by-step process i
 - State update patterns
 - Error handling and recovery
 
-**Total workflows:** 76
+**Total workflows:** 77
 
 ### Agents (`agents/*.md`)
 
@@ -409,11 +409,11 @@ UI-SPEC.md (per phase) ───────────────────
 
 ```
 ~/.claude/                          # Claude Code (global install)
-├── commands/gsd/*.md               # 79 slash commands
+├── commands/gsd/*.md               # 80 slash commands
 ├── get-shit-done/
 │   ├── bin/gsd-tools.cjs           # CLI utility
 │   ├── bin/lib/*.cjs               # 19 domain modules
-│   ├── workflows/*.md              # 72 workflow definitions
+│   ├── workflows/*.md              # 77 workflow definitions
 │   ├── references/*.md             # 35 shared reference docs
 │   └── templates/                  # Planning artifact templates
 ├── agents/*.md                     # 31 agent definitions