htmx 4: doc sweep, example app, and v0.7.0 release

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Part of #18. Last step; depends on all other sub-issues.

Helpers that keep their name but whose semantics or value syntax changed in htmx 4 need their doc comments replaced with the verbatim htmx 4 text and link. Source: https://four.htmx.org/docs/whats-new-in-htmx-4 and the per-attribute pages under https://four.htmx.org/reference/attributes/

## Doc comment sweep

- `Swap`: new styles `textContent`, `delete`, `innerMorph`, `outerMorph`, `outerSync`; aliases `before`/`after`/`prepend`/`append`; `show:`/`scroll:` selector form replaced by `showTarget:`/`scrollTarget:`; new `transition:`, `strip:`, `swapEmpty:` modifiers.
- `Trigger`: `queue:` removed (use `hx-sync`); selectors with spaces are single-quoted (`from:'closest form'`); new `halt`, `capture`, `passive`, `consume`, `target:`.
- `On`: htmx event names changed (`hx-on::before:request`); extended `event -> js; ...` form.
- `Boost`: accepts a config string; default is `outerSync` into ``; boost config outranks explicit `hx-*` attributes.
- `Delete`: no longer includes the enclosing form's inputs.
- `SwapOOB`: OOB swaps now run after the main swap; OOB-only responses skip the main swap.
- `HistoryElt`: history restore re-fetches from the server and selects `[hx-history-elt]`.
- `Target`: `findAll` added to the extended selectors.
- All remaining helpers: replace paraphrased comments with verbatim htmx 4 text per the conventions in `AGENTS.md`.

## Example app

- Update `cmd/example` to htmx 4.0.0 (pinned by the scaffolding sub-issue) and verify the boost + `SetPushURL` flow in a browser against the new `outerSync` body default.
- Note in the README that htmx 4 swaps 4xx/5xx responses by default and re-fetches pages on history navigation, since both change what handlers should return.

## Release

- Tag v0.7.0 with release notes listing removed helpers, the `Disable` meaning reversal, and the header changes.

## Acceptance criteria

- Every exported identifier has a verbatim htmx 4 doc comment with link.
- Example app runs against htmx 4.0.0 and the boost flow works.
- v0.7.0 tagged with release notes.

Start with AGENTS.md and the exported helper doc comments, using the linked htmx 4 documentation as the source for the comment sweep. Then inspect cmd/example and the README, run the example in a browser, and verify the boost plus SetPushURL flow. Done means every exported identifier has a linked verbatim comment, the example works with htmx 4.0.0, and v0.7.0 has release notes and is tagged.

Written by the indexing model from the issue text.