feat(adaptive): support tiered per-ISL TTFT SLO via get_ttft_slo_ms()
- adaptive_bench_lib.sh: add default get_ttft_slo_ms() fallback (flat TTFT_SLO_MS),
use it instead of hardcoded TTFT_SLO_MS in SLO comparison and logs,
add ttft_slo_tiers_desc to run_manifest.json
- glm52_910c config.env: define tiered SLO for GLM-5.2:
≤2048:5000ms, ≤8192:8000ms, ≤32768:12000ms, ≤131072:20000ms, >131072:30000ms
(~70-80% of DSv4-Pro values, since GLM-5.2 has simpler architecture)
- glm52_910c adaptive_config.env: update TTFT_SLO_MS comment noting tiered override
Backward compatible: experiments without get_ttft_slo_ms() keep flat 4000ms behavior.
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