Claude collector: attribute pi usage by provider, not api prefix (#6655)

Pi/omp sessions kept falling into the Claude record when the api
field merely started with 'anthropic'. Kimi and other providers that
speak the anthropic-messages protocol (kimi-coding) were therefore
charged against Claude Code, showing k3 buckets under a Claude tab
even for a user without a Claude login.

Match the codex collector's provider-only attribution: only sessions
whose provider is exactly 'anthropic' count toward Claude usage.

Add a test proving a kimi-coding session sharing the
anthropic-messages api does not land in the Claude record.

Co-authored-by: Luca <luca@itwasarch>

test/shell.d/agent-usage-claude-scanner-test.sh

@@ -112,6 +112,7 @@ mkdir -p "$PI_HOME/.pi/agent/sessions/project" "$PI_HOME/.omp/agent/sessions/pro
 cat >"$PI_HOME/.pi/agent/sessions/project/pi.jsonl" <<EOF
 {"type":"message","id":"pi-1","timestamp":"$timestamp","message":{"role":"assistant","provider":"anthropic","api":"anthropic-messages","model":"claude-pi","usage":{"input":10,"output":4,"cacheRead":3,"cacheWrite":2,"totalTokens":19}}}
 {"type":"message","id":"codex-1","timestamp":"$timestamp","message":{"role":"assistant","provider":"openai-codex","model":"gpt-test","usage":{"input":999,"output":999}}}
+{"type":"message","id":"kimi-1","timestamp":"$timestamp","message":{"role":"assistant","provider":"kimi-coding","api":"anthropic-messages","model":"k3","usage":{"input":999,"output":999}}}
 EOF
 cat >"$PI_HOME/.omp/agent/sessions/project/omp.jsonl" <<EOF
 { "type": "message", "id": "omp-1", "timestamp": "$timestamp", "message": { "role": "assistant", "provider": "anthropic", "model": "claude-omp", "usage": { "input": 20, "output": 5, "cacheRead": 4, "cacheWrite": 1, "totalTokens": 30 } } }