refactor: ponytail audit cleanup (-836 lines, -2 direct deps)

[JustMaris]

Applies the ponytail-audit findings, one commit per finding. The branch removes 836 lines net across 28 files and two direct dependencies (goquery with its cascadia, and google/uuid, which stays only as a transitive dependency of modernc sqlite).

Cuts

• CAPTCHA detection: one detection script instead of eight detector functions. CaptchaInfo keeps only Found and Type; the other fields were never read. Same checks in the same order. The new TestDetectCaptcha has one Chrome fixture per branch. It skips locally without Chrome and runs on CI's Ubuntu runner. I also ran all 9 fixtures in a real browser and they pass.
• Restart-resume of paused web jobs removed: JobPersistence, PersistentJobState, checkPendingJob, resumePendingJob and saveJobProgress are gone. A paused job's remaining list is exactly what "Send all" or automation picks up next anyway. The Brokers page wording is updated, and leftover pending_job*.json files are deleted at startup.
• One inbox scan path: Monitor.ScanAndStore and inbox.RecordReply replace the separate implementations in the CLI monitor, the web scan and the web rescan.
• One send step: email.SendRemoval does render → send → history record for CLI send, the web "Send all" job and the single-broker send.
• History store: one scanner and one column list for broker responses instead of five copies, and GetBrokerResponses builds its WHERE clause instead of carrying four query variants.
• Small ones: RateLimiter loses a cleanup goroutine it didn't need (the key set is fixed), email.SequenceKey context plumbing is gone, goquery is replaced by an x/net/html tokenizer, uuid by crypto/rand.Text().

Bugs fixed along the way

• Web scans could archive the wrong mail. They archived the UIDs of emails fetched from the archive folder too. ArchiveEmails applies UIDs to INBOX, where an archive-folder UID can name an unrelated message. Only INBOX UIDs are archived now.
• Message-ID: sends now carry a real Message-ID: <random@sender-domain> header, and that's what gets recorded. Before, no header was sent and the recorded ID was a local placeholder (%!d(<nil>) for web sends).
• Pipeline status: new replies found by the web scan and by monitor --watch now advance the broker's pipeline status, as eraser monitor already did.
• Unstyled messages: the scan, rescan, reclassify, setup and send-status HTML fragments used Tailwind classes that aren't defined anywhere (there's no Tailwind build), so they rendered unstyled. They now use the layout's .alert, .badge, .btn and text-error/text-warning classes.
• Rescan body backfill: the "fill the body only if it's empty" check always saw an empty body, because the lookup query didn't select the body. It now does.

Behaviour change to note: with auto_archive on, a rescan now archives INBOX replies, the same as a scan.

Verified: go vet ./... && go test ./... pass, and -race on web, inbox and history. New tests cover SendRemoval (sent, failed, and render error), the Message-ID header matching the recorded ID (fake SMTP server), RecordReply (new / seen / reclassified, pipeline advance, profile attribution), HTML href extraction, and the CAPTCHA fixtures. A dry-run eraser auto --once cycle completes.

BEGIN_COMMIT_OVERRIDE
fix(inbox): web scans no longer archive unrelated INBOX messages
fix(email): send and record a real Message-ID header
fix(inbox): new replies from web scans and monitor --watch advance pipeline status
fix(web): scan, setup and send-status messages render with the app's styles
refactor: ponytail audit cleanup (-836 lines, -2 direct deps)
END_COMMIT_OVERRIDE