tasks: fix taskgraph enum values for architecture tasks (level, impact, scope)

The three architecture tasks I seeded in the previous commit used invalid
enum values for the taskgraph frontmatter (level: architecture, impact: local,
scope: small). Corrected to the valid taskgraph enums: level: implementation/
decomposition/planning, impact: project/component, scope: moderate/narrow.
taskgraph validate now passes for tasks/architecture/.

(Pre-existing tasks/call/registry/*.md and tasks/core/ownership-store-trait.md
use status: done instead of completed — out of scope for this fix.)

tasks/architecture/open-questions-decompose.md

@@ -6,7 +6,7 @@ depends_on: []
 scope: moderate
 risk: low
 impact: project
-level: architecture
+level: implementation
 ---
 
 ## Description

tasks/architecture/oq-09-10-blocking-conditions.md

@@ -3,10 +3,10 @@ id: architecture/oq-09-10-blocking-conditions
 name: Add explicit Blocked on conditions to OQ-09 (WASM) and OQ-10 (Git Adapter)
 status: pending
 depends_on: []
-scope: small
+scope: narrow
 risk: low
-impact: local
-level: architecture
+impact: component
+level: decomposition
 ---
 
 ## Description

tasks/architecture/safe-exit-blocker-task-mechanism.md

@@ -6,7 +6,7 @@ depends_on: []
 scope: moderate
 risk: low
 impact: project
-level: architecture
+level: planning
 ---
 
 ## Description