feat: reply from the address a message was delivered to

[salmonumbrella]

Summary

When a message arrives at an alias through a BCC delivery or a catch-all, the alias never appears in To/Cc — so the existing reply alias auto-selection (which matches To/Cc/From against the account's aliases) misses, and the reply comes from the primary address. This follows up on the #256 discussion: "MailFlow doesn't yet auto-select the alias a message was delivered to when you hit reply."

This PR captures the envelope recipient (Delivered-To / X-Delivered-To / X-Original-To / Envelope-To) at ingest and lets the reply alias matcher check it first, ahead of To/Cc/From. Selection stays transient — nothing is auto-created or persisted into aliases, per the direction in #256. Existing messages carry no capture (NULL) and behave exactly as today, then backfill on their next sync touch; the send path is untouched — the matched alias flows through the existing aliasId mechanism.

Changes

• Migration 0035 (IF NOT EXISTS-guarded, numbered after main's current 0034): nullable messages.delivery_addresses JSONB, same shape as list_unsubscribe
• messageParser.js: parseDeliveryAddresses() reads the four delivery headers from the already-parsed header map (reuses parseMailboxList; no IMAP fetch changes), deduped and capped at 50 addresses (sender-controlled input, capped like subject/snippet)
• imapManager.js: persists the parsed addresses at the message INSERT sites with the same COALESCE upsert plumbing as list_unsubscribe (the synthesized sent-copy record has no delivery headers and is deliberately left out)
• messageService.js + mail.js: expose delivery_addresses on the message shapes the frontend actually replies from (list, thread, single message, resolve)
• MessagePane.jsx: the inline reply-alias matcher is extracted to frontend/src/utils/replyAlias.js (pure, testable) and now checks delivery addresses first; the existing To/Cc/From matching semantics — including the alias-creation-order tiebreak for multi-alias accounts — are preserved bit-for-bit and pinned by tests

Testing

• Backend: 633/633 (vitest), lint clean (--max-warnings 0) — new parser cases: repeated/multi-line headers, angle-bracket forms, cross-header dedupe, junk lines, the size cap
• Frontend: 1359/1359 (node --test), lint clean, production build clean — matcher tests pin: delivered-to beats To/Cc, the unchanged multi-alias tiebreak, malformed-JSON safety, case-insensitivity
• No new dependencies; no behavior change for existing messages (NULL capture ⇒ identical selection to today)

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