rule proposal: operator direction

Proposal template

```md
# Rule Proposal - <Slug>
<Short Description>

## Metrics

### Complexity
> _How complex (napkin math) is this rule to implement?_

|Low|Medium|High|
|--|--|--|
|x|||

### Cost of not enforcing
> _How much pain does checking this rule avoid?_

|Low|Medium|High|
|--|--|--|
|x|||

### Auto-Fix Value
> _How tedious is fixing this rule manually?_

|Low|Medium|High|
|--|--|--|
|||x|

### Bikeshed Coefficient
> _How contentious is this rule (with proposed configuration options)?_
> _Examples:_
> * _High bikeshed: `replace-if-with-case` that rejects all `if x then y else z` in favor of `case x of true -> y; false -> z`_
> * _Med bikeshed: `if-else` with config options for `prefer-if-then`, `prefer-guard`, `prefer-case`_
> * _Low bikeshed: `avoid-unsafe-coerce`_

|Low|Medium|High|
|--|--|--|
||x||

## Modes
> _Put configurable modes here as subheadings. If no configuration / only 1 mode, just use "Default."_

## Examples
> _For each configurable mode, provide at least 1 example of "do" and 1 of "don't do."_

### Foo
bar

## Rationale
> _Insert rant here_
```

# Rule Proposal - Operator Direction
Spot mixed-convention use of `$`/`#`, `<<<`/`>>>`, `<$>`/`<#>`

## Metrics

### Complexity
> _How complex (napkin math) is this rule to implement?_

|Low|Medium|High|
|--|--|--|
|||x|

### Cost of not enforcing
> _How much pain does checking this rule avoid?_

|Low|Medium|High|
|--|--|--|
|x|||

### Auto-Fix Value
> _How tedious is fixing this rule manually?_

|Low|Medium|High|
|--|--|--|
|||x|

### Bikeshed Coefficient
> _How contentious is this rule (with proposed configuration options)?_
> _Examples:_
> * _High bikeshed: `replace-if-with-case` that rejects all `if x then y else z` in favor of `case x of true -> y; false -> z`_
> * _Med bikeshed: `if-else` with config options for `prefer-if-then`, `prefer-guard`, `prefer-case`_
> * _Low bikeshed: `avoid-unsafe-coerce`_

|Low|Medium|High|
|--|--|--|
||x||

## Modes
> _Put configurable modes here as subheadings. If no configuration / only 1 mode, just use "Default."_
### `ltr`
Strongly prefer / dogmatically enforce `#`, `>>>`, `>>=`, `<#>`, etc.
### `rtl`
Strongly prefer / dogmatically enforce `$`, `<<<`, `=<<`, `<$>`, etc.
### `rtl-pure-ltr-monad`
Use `rtl` as default, unless expression contains `=<<` or `<=<`; then ltr for that expression

## Examples
> _For each configurable mode, provide at least 1 example of "do" and 1 of "don't do."_

### `ltr`
**Do**
```purs
myNum # Number.trunc # Int.toString # show
strMaybeNum # Number.fromString <#> Milliseconds >>= Instant.instant <#> Instant.toDateTime
```
**Don't**
```purs
show $ Int.toString $ Number.trunc $ myNum
Instant.toDateTime <$> (Instant.instant =<< Milliseconds <$> Number.fromString strMaybeNum)
```
### `rtl`
**Do**
```purs
show $ Int.toString $ Number.trunc $ myNum
Instant.toDateTime <$> (Instant.instant =<< Milliseconds <$> Number.fromString strMaybeNum)
```
**Don't**
```purs
myNum # Number.trunc # Int.toString # show
strMaybeNum # Number.fromString <#> Milliseconds >>= Instant.instant <#> Instant.toDateTime
```
### `rtl-pure-ltr-monad`

**Do**
```purs
show $ Int.toString $ Number.trunc $ myNum
strMaybeNum # Number.fromString <#> Milliseconds >>= Instant.instant <#> Instant.toDateTime
```
**Don't**
```purs
myNum # Number.trunc # Int.toString # show
Instant.toDateTime <$> (Instant.instant =<< Milliseconds <$> Number.fromString strMaybeNum)
```

## Rationale
> _Insert rant here_

Consistent style. Personal dogma is use regular composition / expression order (RTL) except for monadic expressions because bind & kleisli operators have low precedence, making you write **_parentheses_** 🤢

Also monadic expressions tend to have a more linear time-bound nature which lends better to LTR

No files, tests, or entry points are identified in the issue. Review the proposed `ltr`, `rtl`, and `rtl-pure-ltr-monad` modes and their examples first; done would require an agreed implementation of the operator-direction rule, including its configuration behavior and checks.

Written by the indexing model from the issue text.