docs(website): add a self-contained Extend section to the docs site

[benvinegar]

Scoped to extension docs only — the agent-workflows rewrite, README cleanup, and keybindings page live in #635, #636, and #634 for individual review.

The docs site had no extension documentation, and the first cut of this PR only summarized the surface and linked to docs/extensions.md on GitHub for everything real. The site is the docs, so this now ports the full authoring guide into a new Extend sidebar group of four self-contained pages:

• Extensions — what an extension is, discovery order and folder extensions, ids, bundled extensions, the trust model, failure isolation, CLI flags and [extensions] / [extension.<id>] config, and the complete collapse-generated example.
• Extension API — apiVersion, registerTheme, registerFileLanguage, transformChangeset, registerCommand (chords, remapping, the Extensions menu, ctx.selection/navigation/sidebars), dialogs, the lifecycle event table, the hunk.events bus, hunk.config trust caveats, notify, log, and what is not contributable yet.
• VCS adapters — registerVcsAdapter, operations, detection order and priorities, watch signatures/plans, readFileSource, extraFiles, moved lines, and HunkExtensionUserError.
• Custom sidebars — registerSidebarView, props and actions, the injected keybindings manager, pane ownership, the scrollbox ref contract, and event-driven state via useSyncExternalStore.

Content is ported faithfully from docs/extensions.md (the repo guide is unchanged for now — worth deciding separately whether it should slim down to a pointer once this lands, so the two copies don't drift). Also adds an Extend card to the docs index and cross-links from the configuration page. Empty changeset (docs-only).

bun run website:build (29 pages), bun run website:links, and bun run website:check all pass, including anchor validation for the new cross-page links.

🤖 Generated with Claude Code

https://claude.ai/code/session_01KHY9ReVesQXwKdRU47MwJ9

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Project	Deployment	Actions	Updated (UTC)
hunk-web	Ready	Preview	Jul 29, 2026 1:56am

[greptile-apps]

Greptile Summary

Reorganizes Hunk’s documentation around clearer user and agent workflows.

• Condenses the agent workflow guide and designates the generated review skill as the authoritative command reference.
• Moves keybinding and extension guidance into dedicated website pages and adds them to navigation.
• Refocuses the README on quick-start workflows, integrations, and links to hosted reference documentation.

Confidence Score: 5/5

The documentation-only reorganization appears safe to merge.

The changed commands, configuration examples, extension behavior, keybinding guidance, links, and website navigation are consistent with the relevant repository contracts, with no concrete changed-code failure identified.

Important Files Changed

Filename	Overview
README.md	Reorganizes setup, review workflows, integrations, and configuration guidance while linking detailed references.
docs/agent-workflows.md	Condenses the human-facing agent workflow and aligns its examples with the generated skill and session CLI.
website/astro.config.mjs	Adds the new keybindings and extensions pages to the Configure sidebar.
website/src/content/docs/docs/configure/extensions.md	Adds focused documentation for extension discovery, trust, capabilities, and configuration.
website/src/content/docs/docs/configure/keybindings.md	Adds focused documentation for keybinding replacement, conflicts, chord grammar, and user-only scope.
website/src/content/docs/docs/configure/configuration.md	Cross-links configuration guidance to the new keybindings and extensions pages.

_{Reviews (1): Last reviewed commit: "docs: streamline agent integration guide..." | Re-trigger Greptile}