Show send-as address on thread reads

[robzolkos]

Fixes #483.

HEY stores the selected From address in sender, while creator stays the account user. Keep and show the sender in CLI and TUI thread reads.

Red send/read regression now passes; make test and make lint pass. A live dev send succeeded, but dev search returned 500, so live readback was not verified.

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Summary by cubic

Fixes #483. Thread reads now show the actual send-as address HEY recorded, instead of always displaying the account user's address.

Changes

• Retains sender through threadload and displays it in CLI, TUI, HTML, and Markdown output; creator stays the account user.
• Omits sender when the entry's message was not read or on index-only formats (--count, --ids-only).
• Documents the sender field in docs/cli.md, docs/tui.md, and skills/hey/SKILL.md.

^{Written for commit b40768b. Summary will update on new commits.}

[Copilot]

Copilot review overview

🟢 Approved

The only unresolved comment is a non-blocking documentation nit.

Review effort: Balanced
Findings: None

What changed in this PR

Preserves HEY’s selected send-as identity separately from the account creator and displays it in CLI and TUI thread reads.

Changes:

• Retains and accounts for sender metadata.
• Exposes sender identity across CLI and TUI formats.
• Adds regression tests and documentation.

Non-blocking note: update skills/hey/SKILL.md to document the new sender field.

File	Description
internal/​tui/​mail.go	Displays the selected sender identity.
internal/​tui/​mail_test.go	Tests TUI send-as rendering.
internal/​threadload/​threadload.go	Retains and budgets sender metadata.
internal/​threadload/​threadload_test.go	Tests sender retention and budgeting.
internal/​mail/​entry.go	Adds sender data to mail entries.
internal/​mail/​entry_test.go	Tests creator/sender separation.
internal/​cmd/​topic.go	Exposes and formats sender data.
internal/​cmd/​topic_test.go	Tests sender serialization and formatting.
internal/​cmd/​thread_sender_test.go	Adds end-to-end send/read regression coverage.
internal/​cmd/​thread_partial_test.go	Verifies unread entries omit sender metadata.
docs/​tui.md	Documents TUI sender display.
docs/​cli.md	Documents CLI sender semantics.

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[cursor]

Approved: Cursor Security Agent completed with no findings that need human review, and Cursor Bugbot was not running on this PR. No approval-policy files applied, and no prior approval needed re-evaluation. Reviewers were not assigned.

  

_{Sent by Cursor Approval Agent: Pull Request Approver}

[robzolkos]

Fixed - the HEY skill now explains sender and when it is safe to use creator as a fallback.