Add HTML file input and complete draft exports

[jr-lillard]

Summary

• add --message-html-file to compose, reply, forward, bulk reply, and draft editing with regular-file and UTF-8 validation
• add byte-exact draft show --html output and safe ordered attachment metadata
• add all-or-nothing draft export bundles containing exact HTML, safe JSON, and verified attachment downloads, with narrowly guarded same-draft --force replacement
• document the new surfaces in command help, README, and the bundled HEY skill

This branch builds independently against the released HEY SDK v0.27.0 and does not add a module replacement.

Testing

• TMPDIR=/tmp GOWORK=off make release-check
• gitleaks v8.21.2
• coverage floor check: 83.115% (17,081 / 20,551 statements; required 70.8%)
• Linux amd64 and Windows amd64 cross-builds
• ARM64 smoke-test compilation

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Summary by cubic

Adds --message-html-file to compose, reply, forward, bulk reply, and draft edit so raw HTML messages can be read from a local file instead of passed inline, with regular-file and UTF-8 validation. Adds byte-exact draft show --html output with safe attachment metadata, plus a new draft export command that writes an all-or-nothing bundle containing the exact HTML, a JSON manifest, and SHA-256-verified attachment downloads.

New Features

• draft export writes a hey-draft-export/v1 bundle into a new directory and commits it atomically on macOS and Linux, refusing to overwrite an existing one; --force swaps the new bundle in atomically where the OS supports it.
• draft show --json now includes attachment filename, content type, and byte size, without internal locators.
• Documented the new surfaces in command help, README, and the bundled HEY skill.

^{Written for commit 510126f. Summary will update on new commits.}

[Copilot]

Pull request overview

Adds raw HTML file input across email commands and comprehensive local draft export support.

Changes:

• Adds --message-html-file to five email workflows.
• Adds draft HTML output, attachment metadata, and staged export bundles.
• Updates tests, documentation, help, and command-surface snapshots.

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Reviewed changes

Copilot reviewed 32 out of 32 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
.surface	Records new commands and flags.
README.md	Documents HTML input and draft exports.
skills/hey/SKILL.md	Updates bundled agent guidance.
tests/smoke/draft_lifecycle_test.go	Smoke-tests draft HTML and export.
internal/output/writer.go	Updates HTML format documentation.
internal/cmd/topic.go	Updates HTML-fragment commentary.
internal/cmd/thread_reply_test.go	Tests reply HTML-file input.
internal/cmd/root.go	Enables HTML output for draft show.
internal/cmd/reply.go	Adds reply HTML-file input.
internal/cmd/message_html_file.go	Implements validated HTML-file reading.
internal/cmd/message_html_file_test.go	Tests validation and exclusivity.
internal/cmd/journal.go	Uses shared HTML-fragment writer.
internal/cmd/html.go	Adds shared fragment writer.
internal/cmd/html_test.go	Tests fragment output.
internal/cmd/forward.go	Adds forward HTML-file input.
internal/cmd/forward_test.go	Tests forward file input.
internal/cmd/drafts.go	Registers draft export.
internal/cmd/draft.go	Adds HTML output, metadata, and file editing.
internal/cmd/draft_test.go	Tests new draft behavior.
internal/cmd/draft_export.go	Implements staged draft bundles.
internal/cmd/draft_export_test.go	Tests export integrity and replacement.
internal/cmd/draft_export_commit_windows.go	Adds Windows no-replace publishing.
internal/cmd/draft_export_commit_other.go	Adds fallback publishing.
internal/cmd/draft_export_commit_linux.go	Adds Linux no-replace publishing.
internal/cmd/draft_export_commit_darwin.go	Adds macOS no-replace publishing.
internal/cmd/contacts_show.go	Uses shared fragment output.
internal/cmd/contact_note_show.go	Uses shared fragment output.
internal/cmd/compose.go	Adds compose HTML-file input.
internal/cmd/compose_test.go	Tests compose file input.
internal/cmd/bulk_reply.go	Adds bulk-reply HTML-file input.
internal/cmd/bulk_reply_test.go	Tests bulk-reply file input.
internal/cmd/attachments_test.go	Tests HTML-file drafts with attachments.

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