feat(ui): show the VapourSynth calls each pass makes

[StuartCameronCode]

Experts coming from Hybrid, StaxRip or AviSynth recognise FixChromaBleedingMod or MSRCP instantly, and couldn't tell what a VapourBox pass was doing from its labels. Each pass now prints its calls.

Advanced mode only — a plugin name isn't actionable for someone who hasn't asked for that level of detail, and advanced mode is the app-wide lever for exactly that judgement.

Two shapes, because filters come in two shapes

One call per method — the readout names the selected method's own function:

VAPOURSYNTH
core.zsmooth.CCD

This data already existed on all 49 methods and was already parsed by the Dart model. It had simply never been rendered anywhere, so for these passes this was a display gap, not a data one.

Composite passes — Colour Correction, Chroma Fixes and Crop & Resize aren't one call. They now declare an implementation list of the whole repertoire, and the readout emphasises what's running:

VAPOURSYNTH
core.std.Levels        — automatic levels, measured per frame with core.std.PlaneStats
core.std.Expr          — automatic white balance, measured per frame with core.std.PlaneStats
adjust.Tweak           — brightness, contrast, saturation, hue
core.std.Levels        — levels
haf.SmoothLevels       — levels, dithered and limited as it maps
core.retinex.MSRCP     — shadow detail, on the luma plane only

Showing the inactive calls is the point: it says what the pass could do, not only what it's doing now.

Colour Correction was the reported case and is the sharpest one — it has no method dropdown at all (the inert one went in the panel audit), so nothing anywhere in the UI named any of those six.

activeWhen takes more than one key, and that's load-bearing

applyLevels chooses between std.Levels and haf.SmoothLevels, so each is gated on the pair {applyLevels, smoothLevels} and precisely one is ever emphasised. Gating both on applyLevels alone would claim the pass runs two levels operations. Chroma Fixes has the same shape: automatic and manual alignment are both core.resize.Spline36, told apart only by their role text, and automatic supersedes manual exactly as the generator does.

It reuses _checkVisibleWhen rather than adding a second matcher, so the two can't drift.

Placeholders fixed rather than displayed

spotless → spotless.SpotLess, qtgmc_internal → haf.QTGMC (NoiseProcess), whisper → whisper-cli, and havsfunc.ChangeFPS → haf.ChangeFPS (a prefix used nowhere else). custom stays as bookkeeping on the three composite passes but is never shown — asserted.

One judgement call to flag

Crop & Resize's scaling entry reads core.resize.* rather than a concrete kernel, because the kernel is a seven-way enum already visible as its own dropdown directly above; listing all seven greyed out seemed like noise. It's the one entry that isn't a literal callable name. Straightforward to expand into seven activeWhen-gated entries if exactness is preferred.

Testing

820 Flutter tests pass. New:

• 8 widget tests on the readout — advanced-mode gating, following the method rather than the filter, composite emphasis, the two-key applyLevels case in both directions, the automatic/manual Spline36 pair, and placeholder suppression.
• 4 schema lints per filter, each covering a silent failure: blank function, custom without an implementation list, activeWhen naming a non-existent parameter (the call would read as permanently inactive — same failure mode as a visibleWhen naming a missing parameter), and a list where nothing can ever be active.

Documented in docs/FILTER_SCHEMA.md and CLAUDE.md.