chore: bump to 0.5.6 for the discovery liquidity probe

[eaitbrahim]

Bumps pyproject.toml and all four workspace members 0.5.5 → 0.5.6, plus uv.lock. Same shape as #184.

Why now

assets discover --probe-liquidity and screen.median_daily_quote_volume landed on main in #188 but are in no release, so the deployment — running keel 0.5.5+7b02bfd8fbbc [release] — cannot run them. The keel-asset-scout skill has been updated to make the probe the first step of every sweep, which fails outright against 0.5.5. This closes that gap.

What 0.5.6 contains

The discovery pre-filter now measures what the admission gate measures. assets discover filtered on the venue's reported 24h quote volume while assets screen admits on the median of volume × close over cached history — same units, different statistics, and the gap changes outcomes in both directions:

• BICO was shortlisted on a reported $12.81M/24h and then rejected by the screen at a median daily volume of 108,004 — 9× under the floor, a 227× gap between the two numbers.
• DOGE was nearly dropped for sitting 1.7% below the $5M discovery floor when, on the admission criterion, it is ~30× above it.

screen.median_daily_quote_volume is now the single definition of the statistic (cli._market_facts had it inline; a second copy next to discover would drift, and that drift is the bug). --probe-liquidity samples 180 days of daily candles per candidate — one extra request, same cost model as --probe-history — and marks LOW/ok against the same floor screen_asset applies.

Against the live venue it catches BICO (36,137) plus two the old filter passed straight through: IMU (71,713) and GWEI (440,864). Three of the top fourteen by 24h volume are sub-floor on the real criterion.

It is an estimator, not a verdict, and the output says so: 180 days recent vs the screen's full cached history. ZEC probes 33.1M against a full-history median of 1.23M — a 27× spread from a recent surge. ok means "worth pulling candles for", never "will be admitted". A recent window also makes a false LOW unlikely for a currently-active asset, which is the safe direction for a pre-filter.

No behaviour change to the gate itself — same criterion, same floor, same verdicts.

Verification

• 2137 passed, ruff clean, mypy clean across 203 source files
• keel --version → 0.5.6+9dcccadb6939 on this branch

Note on #188

#188 squash-merged the code change together with the docs/experiments harness, so its title and body describe only the research work. Its body is what scripts/release_notes.py will inline for 0.5.6, so it has been edited to describe the code change that actually shipped in it.

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