docs(fv-ml1): reconcile GPU seat inventory and model lineage against running containers

Read from docker inspect, nvidia-smi and each model's own config.json rather
than from compose files or the gateway config, so the document records what is
deployed rather than what was intended.

Findings worth naming:

- char-rp drift. The LiteLLM config documents char-rp as G4-MeroMero-v2-31B on
  ana-ml2 GPU 0; :8016 actually serves gemma4-26b-a4b-it-nvfp4, a 26B 30-layer
  128-expert stock Gemma-4, on fv-ml1 GPU 1. Host renaming explains part of it,
  but 31B MeroMero-v2 and 26B stock gemma4 are different models and the comment
  block carries sampler defaults keyed to the model it names.
- Two gateway aliases are dead: erp-tune-v2 (:8098) and gemma4-26b-a4b-it-base
  (:8099). Nothing is listening on either; callers get a connection failure
  rather than a clear retirement error.
- Three different speculative-decoding methods coexist -- dflash k=7 with a
  separate drafter on mog-sec, qwen3_5_mtp k=3 on gen, mtp k=3 on flash-next.
  The method string is architecture-specific; copying a --speculative-config
  between seats without changing it will not work.
- Three seats run the floating :latest tag, so what they would pull on recreate
  is not what is running and was never recorded.
- Seven aliases resolve to vllm-gen on :8015, which is why GPU 0 shows draw
  during ordinary OpenWebUI use -- its auto-titling fires summarizer per turn.

Also commits the flash-next-seat MTP k=3 change made today: compose gains the
speculative-config with its measured rationale, and .env.example documents the
KV-cache reduction MTP requires (14 GiB OOMs, 10 GiB verified in production).

stacks/flash-next-seat/compose.yaml

@@ -221,14 +221,40 @@ services:
       # the mog-sec seat uses.
       - --tool-call-parser
       - ${FN_TOOL_CALL_PARSER:-qwen3_xml}
-      # ── NO --speculative-config LINE, ON PURPOSE ─────────────────────────────
-      # Speculative decoding is absent rather than disabled-by-a-flag, because
-      # there is no honest "off" value for --speculative-config and a placeholder
-      # flag in this slot is the kind of thing that gets copied forward and
-      # misread. To turn MTP on, add these two lines here and nothing else:
-      #     - --speculative-config
-      #     - '{"method": "mtp", "num_speculative_tokens": 3}'
-      # Read the MTP warning in the header first; the measured default is off.
+      # ── MTP ON, k=3 — MEASURED 2026-09-13, reversing the previous default ────
+      # This seat shipped with speculative decoding absent, citing vLLM's recipe:
+      # on 4xH100 at TP=4 that recipe measured MTP WORSE at every concurrency
+      # (8-36% lower throughput, ~36% acceptance) and said don't default it on.
+      #
+      # That recipe does not describe this machine, and the campaign in
+      # services/flash-next-mtp-bench/ measured close to its inverse on 1x RTX
+      # PRO 6000 Blackwell at TP=1 (5 arms x 3 reps x conc 1/4/8, drift-bracketed
+      # by a no-spec arm at each end, both within noise):
+      #
+      #     vs no-spec floor   conc=1    conc=4    conc=8    acceptance
+      #     k=1                +29.6%    +40.7%    +27.2%    ~73%
+      #     k=2                +42.3%    +52.4%    +37.7%    ~59%
+      #     k=3                +52.1%    +51.3%    +33.5%    ~48%
+      #
+      # k=3 is set because this seat is single-user interactive, where conc=1
+      # dominates and k=3 measured best (+52.1%, and the k3-over-k2 margin at
+      # conc=1 cleared its own noise floor). For a batch-heavy seat prefer k=2:
+      # it is best or statistically tied everywhere, and k=3's conc=4/8 figures
+      # sit BELOW k=2 (within noise, so not a proven regression, but no gain).
+      #
+      # ⚠ TWO COSTS, both measured, neither optional:
+      # 1. MTP adds ~5.08 GiB of draft-head weights (74.36 -> 79.44 GiB) and
+      #    raises per-token KV cost ~16% (26.24 -> 30.47 KiB/token). The seat's
+      #    previous 14 GiB FN_KV_CACHE_MEMORY OOMs at engine init with MTP on.
+      #    FN_KV_CACHE_MEMORY must come down; see .env.example.
+      # 2. Run-to-run variance grows sharply with k (within-arm spread at conc=4:
+      #    5.69 no-spec -> 34.61 k1 -> 57.06 k2 -> 76.90 k3). Throughput is
+      #    higher and LESS predictable. That is a real operational property.
+      #
+      # To turn MTP back off, delete these two lines — do not add a placeholder
+      # value, there is no honest "off" for --speculative-config.
+      - --speculative-config
+      - '{"method": "mtp", "num_speculative_tokens": 3}'
     deploy:
       resources:
         reservations: