feat(gateway): G8 part b — typed blocker_type + what_needed on i_am_blocked

Pre-gateway parity (G8 part b of the 2026-05-11 design). The pre-gateway
TaskBlockInput at 254cc93:roboco/mcp/schemas/__init__.py required
blocker_type (external|internal|question|dependency) and what_needed
so PMs could triage their inbox by class. Current i_am_blocked dropped
both fields — every blocked task looked the same to the PM.

Now i_am_blocked accepts both as optional kwargs:
- Back-compat: callers that omit them still work (blocker_type defaults
  to None → rendered as flat reason in the struggle entry).
- New: when supplied, the struggle journal entry body is structured
  markdown (## Blocker Type / ## What Needed sections) so the panel's
  journal view renders named blocks instead of one flat sentence.

Validator on blocker_type enforces the enum at the Pydantic boundary
with a clear "must be one of: ..." error if the agent invents a value
(same pattern as the Wave 3 G7 validators).

G8 part a — typed `pause(checkpoint_summary, remaining_work)` — defers.
That gap needs a new IntentSpec in foundation/policy/lifecycle.py
(currently pause is an ActionSpec only; agents auto-pause via i_am_idle)
plus checkpoint wiring through TaskService.add_checkpoint. Material
work, deferred until after the user has deployed and verified G7 +
G8b lands cleanly.

Wired:
- roboco/api/schemas/v2/flow.py — IAmBlockedRequest gains optional
  blocker_type + what_needed; @field_validator enforces the enum
- roboco/api/routes/v2/flow_dev.py — passes the new fields through
- roboco/services/gateway/choreographer/_impl.py — i_am_blocked signature
  + structured struggle-entry rendering
- roboco/mcp/flow_server.py — typed wrapper with the kwargs
- agents/prompts/roles/developer.md — updated verb table
- tests/unit/mcp_servers/test_flow_server.py — updated to expect the
  new optional kwargs as None when omitted

Quality: ruff + mypy clean. 505 tests pass.

tests/unit/mcp_servers/test_flow_server.py

@@ -184,7 +184,16 @@ def test_i_am_blocked_sends_reason(flow_module: types.ModuleType) -> None:
 
     assert result == {"status": "blocked"}
     _, kwargs = fake_client.post.call_args
-    assert kwargs["json"] == {"task_id": "task-xyz", "reason": "waiting for env var"}
+    # Pre-gateway parity (G8): i_am_blocked now also carries optional
+    # blocker_type / what_needed — when caller omits them the wrapper
+    # forwards `None` so the backend can fall back to the default
+    # 'internal' classification.
+    assert kwargs["json"] == {
+        "task_id": "task-xyz",
+        "reason": "waiting for env var",
+        "blocker_type": None,
+        "what_needed": None,
+    }
 
 
 def test_i_am_idle_posts_empty_body(flow_module: types.ModuleType) -> None: