fix: ListModels returns empty on network error, reduce MaxOutput to 2000 (closes #5, closes #7)

[jpleva91]

Summary

• Bug bug: listModels() in ollama.ts throws on network error instead of returning empty #5: ListModels() in internal/ollama/client.go now returns ([]string{}, nil) instead of (nil, err) when the HTTP request fails due to a network/connection error. This prevents callers from crashing when Ollama is unreachable — they simply get an empty model list. Valid HTTP error responses (e.g. 401) still propagate as before.
• Bug bug: qa-agent reads files with no size guard — large files blow out Ollama context window #7: Reduced MaxOutput constant in internal/tools/tools.go from 8000 to 2000 chars. With 5 tool calls, the previous limit could produce 40,000 chars of aggregate output, blowing past small Ollama context windows (4096 tokens). At 2000 chars per file, the aggregate stays within budget for the default context size.

Test plan

• go build ./... passes
• go test ./... passes (no test files in affected packages)
• Manual: confirm ListModels() returns empty list when Ollama is stopped
• Manual: confirm qa-agent stays within context window with 5-file reads

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