GeezerVison

## Description
Adds the **Argument picks the state** category (codebook C3.1) and a
hint for it. These errors had no useful hint before: a transition that
depends on an argument isn't part of the state machine, so the existing
hints can't explain it.

- Each object instance now records the last call that changed its state
(`StateChange`). Method calls and constructors record their own call,
and state-preserving calls keep the previous record. A join of branches
records nothing, which ends the search below.
- `DecidingArgument` follows that chain back to the last call that
changed a state set the failing call checks. If that call's transition
depends on its arguments or result, the SMT solver looks for values that
would have allowed the failing call: the state before the call, the
call's `to` with its parameters left free, and the failing call's
`from`. The model gives the values for the hint.
- When such values exist, the category comes before the other state
categories. The error then gets only the deciding hint. If none exist,
the error keeps its other category (for example
`ErrorArgumentCannotPickTheState`).

## Example
```
State Refinement Error: found empty(buffer) but expected filled(buffer)

Hints:
  - buffer.reset(boolean) on line 20 decides the state of buffer: with keep == true, this call would be allowed
```
Category: Argument picks the state (C3.1).

## Measured against the codebook
Same runs as #418:
- **Corpus:** 94 of 99 right (91 before), 1 wrong, 4 with no category.
- **Exercises:** 42 of 52 right (34 before), 6 wrong, 4 with no
category.

The category now finds 12 of the 15 C3.1 cases. The ones it misses:
- a guard in `from` that changes no state;
- an earlier value that is the real cause;
- a returned value at a join.

## Type of change
- [x] New feature

## Checklist
- [x] Added tests:
- `ErrorArgumentPicksTheState`, `ErrorConstructorArgumentPicksTheState`
and `ErrorArgumentPicksTheStateEarlier` (the decider is found past a
call on another state set);
- `ErrorArgumentCannotPickTheState` (no value helps, so no category
change);
  - cases in `TestErrorCategories` and `TestStateHints`.
- [x] `mvn test` passes locally

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 5.5 <[email protected]>

… on hover (#171)

Part of #170.

## Why
Focus mode dimmed the methods unrelated to a state error but kept their
text, so the layout did not move (#158). On a large machine the dimmed
label stacks still took the space. In the UDP chat client the state the
error is about, `closed`, was below the fold.

## What
In focus mode:
- **Collapse.** The dimmed methods of each label become a count:
`receive` + `+9 more`, or `2 methods`. Overloads count once. A single
dimmed method keeps its name and conditions.
- **List on hover.** Hovering a count lists its methods, with their
conditions, next to the label. A click keeps the list open until the
next click, a pan or a zoom. The diagram is not laid out again, so the
list appears at once. The list goes right, left, above or below the
label, or beside the diagram at the label's height: wherever it covers
the fewest states, labels and transition lines, and the closest such
place on a tie.
- **Constructors.** The constructors of each state are merged into one
arrow, e.g. `4 constructors`.
- **Layout.** The diagram is laid out again. A tall diagram is shrunk to
fit the panel, but never below 60%.
- **Bright.** Only the failed method stays bright.
- **States.** No state is removed.

**Show all** is unchanged.

An earlier version of this PR also drew a dashed "way to an expected
state": a shortest path along the diagram's transitions. It was dropped.
The path ignores the transitions' conditions and the code, and for a
state that no call leaves (`closed`) it could only suggest creating a
new object. The ways to fix now come from the verifier's hints only
(#172).

Error categories (liquid-java/liquidjava#418) are not used to choose
what to show. #170 explains why.

## Screenshots
Real verifier output (0.0.36) in headless VS Code.

**UDP chat client** (`E_OSS_A1_22`): `receive` after an `if` that may
close the socket. In the screenshots, the three `from = "closed(this) &&
connected(old(this))"` preconditions are removed from the DatagramSocket
spec. With them, verifier 0.0.36 sends no state context or hints for
this error, and the view can only say "Invalid method call at line 28".
That is a verifier issue, separate from this PR.

| Before | After |
|---|---|
| <img
src="https://raw.githubusercontent.com/liquid-java/vscode-liquidjava/pr-screenshots/focus-collapse/udp-before.png"
width="440"> | <img
src="https://raw.githubusercontent.com/liquid-java/vscode-liquidjava/pr-screenshots/focus-collapse/udp-after-v2.png"
width="440"> |

**On hover**, placed off the states and transitions: `+12 more` next to
`bound` goes beside the diagram, `+16 more` next to `connected` to its
right, and the `2 methods` of `ImageWriteParam` left of `tilingExplicit`
and right of `setTiling`.

| UDP, `bound` | UDP, `connected` |
|---|---|
| <img
src="https://raw.githubusercontent.com/liquid-java/vscode-liquidjava/pr-screenshots/focus-collapse/udp-hover-bound.png"
width="440"> | <img
src="https://raw.githubusercontent.com/liquid-java/vscode-liquidjava/pr-screenshots/focus-collapse/udp-hover-connected.png"
width="440"> |

| ImageWriteParam, bottom | ImageWriteParam, middle |
|---|---|
| <img
src="https://raw.githubusercontent.com/liquid-java/vscode-liquidjava/pr-screenshots/focus-collapse/iwp-hover-bottom.png"
width="440"> | <img
src="https://raw.githubusercontent.com/liquid-java/vscode-liquidjava/pr-screenshots/focus-collapse/iwp-hover-middle.png"
width="440"> |

**ImageWriteParam**: `setTiling` from `startTiling`.

| Before | After |
|---|---|
| <img
src="https://raw.githubusercontent.com/liquid-java/vscode-liquidjava/pr-screenshots/focus-collapse/iwp-before.png"
width="440"> | <img
src="https://raw.githubusercontent.com/liquid-java/vscode-liquidjava/pr-screenshots/focus-collapse/iwp-after-v2.png"
width="440"> |

<details><summary>Show all (unchanged)</summary>

<img
src="https://raw.githubusercontent.com/liquid-java/vscode-liquidjava/pr-screenshots/focus-collapse/udp-show-all.png"
width="440">
</details>

The collapsed "Ways to fix" section in the screenshots comes from the
stacked PR.

## Tests
- `npm run test:unit`: 123 passed. New tests cover collapsing, the list
on hover, pinning it with a click and closing it on a click, pan or
zoom, placing it off the states, labels and lines and inside the panel,
merging constructors and the entry transitions from #169, the fit to the
panel, and Show all being unchanged.
- `tsc -p tsconfig.test.json` and `npm run lint`: clean.
- `npm test` (VS Code): 9 + 1 passing, and server `mvn test`: 35
passing, both run on the stacked branch, which includes this one.

Rebased on #169. In focus mode, entry transitions are dimmed and merged
per state, the same way constructors are.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Claude Opus 5.5 <[email protected]>