UI: replace Lucide icons with Papicons

Swap the inline SVG icons of the web UI (top bar, view mode, time range,
export, close, empty state, back to top, settings tabs, save, delete,
lock) for their Papicons equivalents (MIT, Association Papillon).
Papicons are filled shapes: they carry class "pi", which sets
fill: currentColor and no stroke, so the stroked Lucide icons that stay
(zoom out, Docker badge) are unaffected. Add THIRD_PARTY_NOTICES.md with
the Papicons MIT notice and a pointer from both READMEs.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

THIRD_PARTY_NOTICES.md

@@ -0,0 +1,39 @@
+# Third-party notices
+
+## Papicons
+
+Most UI icons (inline SVG with `class="pi"` in `web/index.html`, `web/login.html` and
+`web/app.js`) come from Papicons: https://github.com/PapillonApp/papicons
+
+```
+MIT License
+
+Copyright (c) 2025 Association Papillon
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
+```
+
+## Lucide
+
+The few icons Papicons has no equivalent for (zoom out in the time range bar, Docker source
+badge) come from Lucide (ISC license): https://github.com/lucide-icons/lucide/blob/main/LICENSE
+
+## Fonts
+
+The bundled fonts are covered by the license files next to them in `web/fonts/`.