fix(sight): match latency agents case-insensitively

[yefuyou]

Summary

Correctness follow-up to #2578, discovered during review of #2586.

The existing Agent Sessions UI treats casing variants such as Qoder and qoder as the same Agent, but the latency API used a case-sensitive SQLite comparison. This could make the selected sessions match while /api/metrics/latency returned no rows.

Changes

• make filtered latency Agent matching case-insensitive with SQLite COLLATE NOCASE
• aggregate casing variants into one filtered latency summary
• use the requested Agent casing as the returned agent_name label
• keep process_name fallback semantics unchanged

Scope

This PR is limited to src/agentsight/src/storage/sqlite/genai/stats.rs.

It does not change:

• frontend code
• source filtering
• auxiliary-call scope
• metric formulas or percentile semantics
• null semantics
• schema or eBPF code

Merge order

Recommended order: #2583 → this follow-up → #2586.

#2583 is preferred first because it addresses the existing AgentSight Clippy failures and also touches stats.rs; it is not a hard dependency of this PR. #2586 has the functional dependency on this case-insensitive latency filtering.

Validation

• targeted casing regression test passed
• latency_tests: 9 passed
• latency handler test: 1 passed
• cargo +1.89.0 fmt --all -- --check
• git diff --check
• full unit/integration tests passed
• cargo test has one unrelated existing doctest failure in src/genai/helpers.rs
• Rust 1.89 Clippy is blocked by the two existing lint issues addressed separately by fix(sight): address latency metrics CI follow-ups #2583:
  • clippy::let_and_return in src/agentsight/src/analyzer/unified.rs
  • clippy::unnecessary_map_or in src/agentsight/src/storage/sqlite/genai/stats.rs

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[chengshuyi]

LGTM. 核心逻辑正确，scope 干净。几点 minor suggestions 不阻塞合入：1) 同文件 get_token_timeseries/get_model_timeseries 仍为 case-sensitive，建议 follow-up 统一；2) ?3 COLLATE NOCASE 冗余可简化；3) 可补 process_name fallback 的 case-insensitive 测试。