htmx 4: remove and rename attributes

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Part of #18. Source: https://four.htmx.org/docs/whats-new-in-htmx-4 (Renames and Removals).

## Remove

| Helper | Reason |
|---|---|
| `Ext` | `hx-ext` removed; extensions load via ``. |
| `Disinherit` | Inheritance is explicit in htmx 4. |
| `History` | No localStorage history cache. |
| `Params` | Removed; use the `htmx:config:request` event. |
| `Request` | Replaced by `hx-config` (added in the new-attributes sub-issue). |
| `Prompt` | Moved to the `hx-prompt` extension; extensions are out of scope. |
| `DisabledElt` | Renamed to `hx-disable`, see below. |

## Rename with reversed meaning

- `hx-disable` now means what `hx-disabled-elt` meant: disable elements during a request. `Disable(v string)` keeps its name but gets the new meaning and the new doc comment. https://four.htmx.org/reference/attributes/hx-disable
- Old `hx-disable` (skip htmx processing) is now `hx-ignore`. Add `Ignore()` (bare attribute, no value). https://four.htmx.org/reference/attributes/hx-ignore

Call the meaning reversal out in the release notes for v0.7.0; it is the one change that silently breaks a template that compiles.

## Acceptance criteria

- The seven helpers above are removed, with their tests.
- `Disable` doc comment and test reflect the new semantics.
- `Ignore` exists with test and `Example`.
- `go vet` and tests pass.

Start by locating the seven named helpers and their tests, then inspect Disable and the existing hx-disable behavior. Remove the listed helpers, add Ignore with its test and Example, update Disable's semantics and documentation, and record the reversal in the v0.7.0 release notes. Run go vet and the full test suite to verify completion.

Written by the indexing model from the issue text.