test: trim more Windows hotspot fixtures

[ScriptedAlchemy]

Summary

• add a no-memory dashboard fixture path for project/static/empty-state tests
• reduce oversized LCM fixture payloads while preserving truncation and diagnostic-cap coverage
• avoid indexing in the ambiguous graph selector test and trim serial automation polling
• split savings fixtures so ledger-only and daily-limit tests do not seed the full base dataset twice

Verification

• cargo fmt --all -- --check
• git diff --check
• CARGO_TARGET_DIR=/tmp/tracedecay-target/windows-junit-hotspots-3 cargo test -p tracedecay mcp::tools::handlers::tests::graph_reader_selector_rejects_ambiguous_project_basename -- --nocapture
• CARGO_TARGET_DIR=/tmp/tracedecay-target/windows-junit-hotspots-3 cargo test --test mcp_handler_test lcm_doctor_clean_apply_deletes_all_matching_noise_beyond_diagnostic_samples -- --nocapture
• CARGO_TARGET_DIR=/tmp/tracedecay-target/windows-junit-hotspots-3 cargo test --test mcp_handler_test lcm_session_handlers_expose_bounded_read_apis_and_placeholders -- --nocapture
• CARGO_TARGET_DIR=/tmp/tracedecay-target/windows-junit-hotspots-3 cargo test --test mcp_handler_test lcm_large_json_response_stays_parseable_after_truncation -- --nocapture
• CARGO_TARGET_DIR=/tmp/tracedecay-target/windows-junit-hotspots-3 cargo test --test dashboard_api_test -- --nocapture
• CARGO_TARGET_DIR=/tmp/tracedecay-target/windows-junit-hotspots-3 cargo test --test dashboard_projects_api_test -- --nocapture
• CARGO_TARGET_DIR=/tmp/tracedecay-target/windows-junit-hotspots-3 cargo test --test dashboard_savings_api_test savings_ledger_endpoints_reflect_seeded_ledger -- --nocapture
• CARGO_TARGET_DIR=/tmp/tracedecay-target/windows-junit-hotspots-3 cargo test --test dashboard_savings_api_test daily_model_series_limits_days_not_model_rows -- --nocapture
• CARGO_TARGET_DIR=/tmp/tracedecay-target/windows-junit-hotspots-3 cargo test --test dashboard_savings_api_test session_costs_label_actual_vs_tokenized_vs_estimated -- --nocapture
• CARGO_TARGET_DIR=/tmp/tracedecay-target/windows-junit-hotspots-3 cargo test --test dashboard_automation_api_test dashboard_session_and_skill_runs_emit_activity_when_evidence_is_unavailable -- --nocapture

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Latest commit: 45ce42a

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