feat(pebble): send ntfy title as native UTF-8 via RFC 2047

[ClaydeCode]

Summary

• Background: fix(pebble): ASCII-coerce ntfy title; disambiguate STT against KB folders #73 stopped the silent UnicodeEncodeError on the ntfy Title header by ASCII-coercing the title (em dash → `-`, smart quotes → `'`, etc.). Correct in the moment, but lossy — emoji disappear, German umlauts (`Müller`) collapse to `?`, and Claude has to mentally avoid Unicode in summaries.
• Change: Send the title as native UTF-8. httpx still serialises header values as latin-1, but ntfy accepts RFC 2047 encoded-words (`=?utf-8?[bq]?...?=`) and decodes them server-side. Encoding happens at header-construction time via stdlib `email.header.Header`.
• Preserved: `NotificationPayload.title` keeps the raw Unicode string. The `pebble.notify_title` OTel span attribute also keeps the raw Unicode, so traces stay readable. ASCII titles pass through verbatim — no wire overhead, no behaviour change for framework fallback titles (`Pebble: timeout`, etc.).
• Rejected alternative: ntfy's JSON publish endpoint would side-step header encoding entirely, but it changes the request shape and loses the natural headers↔kwargs mapping. RFC 2047 is a stdlib one-liner.

Test plan

• `uv run pytest` — 371 passed (3 new round-trip tests for em dash, emoji, German umlauts; plus a Unicode clamp test)
• Round-trip verification in tests: encoded header is ASCII-only AND `decode_header` returns the original string
• Manual after deploy: pebble that produces a title like `"Müller — Notiz gespeichert"` should arrive on the watch with characters intact, and `data/logs/traces.jsonl` should show `pebble.notify_ok=true` plus the raw title in `pebble.notify_title`

🤖 Generated with Claude Code