Fix: Narrow complex scenario keywords to prevent false-positive routing

[hllqkb]

Problem

The scenario router was sending almost every Claude Code turn to the complex model (GLM-5.1) instead of default (Kimi K2.6) or think (GLM-5.2).

Root cause: hasComplexPattern matched a broad set of keywords (error, debug, bug, build, create, bash, execute, implement, ...) that appear constantly in tool_result content (bash output, file contents, stack traces) and ordinary coding messages. Since tool_result blocks have role=\"user\" in the Anthropic API, the latest-user-message scan matched on them almost every turn.

Log evidence (before):
```
scenario=complex model=glm-5.1 tokens=19352 # routine coding turn
scenario=complex model=glm-5.1 tokens=44911 # routine coding turn
scenario=default model=kimi-k2.6 tokens=386 # only "hi"-style greetings hit default
```

Fix

Narrow hasComplexPattern to genuinely architectural / large-scale keywords only:

• Kept: architect, architecture, refactor, redesign, complex, difficult, challenging, optimize, performance, efficiency, design pattern, best practice
• Removed: bug, debug, error, exception, stack trace, execute, run command, bash, shell, implement, build, create, add feature, write to, edit file, create file

Routine coding/debugging tasks now stay on default (Kimi K2.6); reasoning-heavy turns still hit think (GLM-5.2) via hasThinkingPattern; only true architectural work routes to complex (GLM-5.1).

Log evidence (after, same workload):
```
scenario=default model=kimi-k2.6 tokens=58588
```

Tests

• go build ./... passes
• go test ./... passes
• Updated two tests whose assertions relied on debug/bug as complex triggers:
  • TestDetectScenario_DebugWithoutVisualIntentStaysTextComplex → renamed to ...StaysTextDefault
  • TestRouteForStreaming_VisionComplexKeepsVisionComplexScenario now uses refactor to exercise the vision_complex path

Backward compatibility

No config options, public APIs, or SPI contracts changed. Only the internal keyword list for scenario detection was narrowed.