feat(ingest-docs): add /gsd-ingest-docs workflow and command

Orchestrator for the ingest pipeline (#2387):

- commands/gsd/ingest-docs.md — /gsd-ingest-docs command with
  [path] [--mode] [--manifest] [--resolve] args; @-references the
  shared doc-conflict-engine so the BLOCKER gate semantics are
  inherited from the same contract /gsd-import consumes.

- get-shit-done/workflows/ingest-docs.md — end-to-end flow:
    1. parse + validate args (traversal guard on path + manifest)
    2. init query + runtime detect + auto mode-detect (.planning/ presence)
    3. discover docs via directory convention OR manifest YAML
    4. 50-doc cap — forces --manifest for larger sets in v1
    5. discovery approval gate
    6. parallel spawn of gsd-doc-classifier per doc (fallback to
       sequential on non-Claude runtimes)
    7. single gsd-doc-synthesizer spawn
    8. conflict gate honoring doc-conflict-engine safety rule —
       BLOCKER count > 0 aborts without writing PROJECT/REQUIREMENTS/
       ROADMAP/STATE
    9. route to gsd-roadmapper (new) or append-to-milestone (merge),
       audits roadmapper's required PROJECT.md fields and only prompts
       for gaps
   10. commit via gsd-sdk

Updates ARCHITECTURE.md counts (commands 80→81, workflows 77→78,
agents tree-count 31→33).

--resolve interactive is reserved (explicit future-release reject).

Refs #2387

Co-Authored-By: Claude Opus 4.7 (1M context) <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:** 80
+**Total commands:** 81
 
 ### 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:** 77
+**Total workflows:** 78
 
 ### Agents (`agents/*.md`)
 
@@ -409,14 +409,14 @@ UI-SPEC.md (per phase) ───────────────────
 
 ```
 ~/.claude/                          # Claude Code (global install)
-├── commands/gsd/*.md               # 80 slash commands
+├── commands/gsd/*.md               # 81 slash commands
 ├── get-shit-done/
 │   ├── bin/gsd-tools.cjs           # CLI utility
 │   ├── bin/lib/*.cjs               # 19 domain modules
-│   ├── workflows/*.md              # 77 workflow definitions
+│   ├── workflows/*.md              # 78 workflow definitions
 │   ├── references/*.md             # 35 shared reference docs
 │   └── templates/                  # Planning artifact templates
-├── agents/*.md                     # 31 agent definitions
+├── agents/*.md                     # 33 agent definitions
 ├── hooks/
 │   ├── gsd-statusline.js           # Statusline hook
 │   ├── gsd-context-monitor.js      # Context warning hook